Serious Sam was the most first-person shooting first-person shooter in the world (even if you were mad enough to try and play it in the third-person mode). Serious Sam 2 is the same game, but prettier, madder, bigger and packed full of more options, so is obviously not nearly as good.
Let me explain.
Let's play alternate history.
This game could be one - maybe two - marks better if we could get another time machine. Instead of going to work for Valve doing whatever it is he's doing, Chet OldManMurray worked on this. Erik can stay at Double Fine, because we don't want to lose any bits of Psychonauts he may have been responsible for. We'll package up Chet, send him back through history and off to sunny Croatia where he can wave a little of his game-deconstruction/scatological magic all over this. And it'd be a better game.
At the very least they'll have an expert in the use of crates on hand.
(Or was Erik the only funny one? I don't think so. It's been a long time.)
Serious Sam was notable for its virtual lack of plot. There was probably one, of course, but it kind of disappeared beneath an endless wave of enormous bull-like beasts. With a bigger budget - pretty much the first gag in the game notes the fact - they've gone and added one, along with much more of the often funny, if slightly-self-indulgent humour which was present in the first. But while that was done as an aside in the first, now similar gags are presented in cut-scenes. They're amateurishly done, often killing the jokes even when they are funny. And, even when they work, they break up Sam's momentum.
If they were to really stress The Funny in cut-scenes, they needed someone funnier to do them. In other words, our time-travelling Chet. Also, while Chet was there, we can hope he'd point out every time that they were losing the plot. Serious Sam 2 isn't quite just another shooter - its personality is entirely unavoidable - but occasionally comes worryingly close. In the same way that Far Cry was worst when simply aping Half-Life and Doom ("The best first-person shooters have moody interior bits. We must do a bit, to show that we too are master FPS designers!") rather than doing the original and thrilling outdoors thing, when Serious Sam 2 lobs in vehicles, gun turrets or cut-scenes it doesn't work. We've seen these before, and their appearances here are distinctly half-hearted. While the explosion physics are impressive, that they don't noticeably effect the vehicle you're driving leaves us distinctly nonplussed every time we're forced to drive one.
When the formula isn't being fiddled with, though, it still presses the buttons Serious Sam did. When it was released, Serious Sam was often described as a retro-throwback to Doom (in terms of numbers of opponents) and Duke Nukem (in its cheery comedy attitude). It wasn't quite true. There had never really been a shooter like Sam when it came out - it was so shamelessly relentless, taking as much from Robotron in its trap-you-in-room-and-here-they-come design as anything more modern. While FPSs are generally renowned for their delight in inspiring claustrophobia, Serious Sam was the agoraphobic's nightmare. This created a different rhythm to play, stressed by Croteam's gleeful disregard for anything approaching realism. Doom III's Monster In The Closet design mainly caused eye-rolling due to the hyper-real world it was trying to portray. In Sam, when you blow up a crate to reveal a monster was hiding in it, you accept it as you do in the way that you do Gold Coins appearing in Super Mario or whatever. Spawning monsters into attack positions is something for you to react to and kill, not something to break atmosphere.
No one asks where the Space Invaders are coming from. If Serious Sam was (and is) a throwback to anything, it's a throwback to games ten years earlier than what's normally cited.
In Sam 2 there are a variety of locations far beyond the original game (or its half-sequel, The Second Encounter). In your quest to collect all five parts of a medallion required to defeat the still brilliantly-named Notorious Mental, the five planets you pass through are wildly different. From the opening world which shares a similar South-American Amazon feel to the mother game, on through the micro-worlds, gloriously weird re-imaginings of the East, Tim-Burton Skeleton-pop-horror, Shrek-esque mock fantasy and... oh, it goes for it, and everything's as colourful and overblown as you could wish.
In a world where first-person shooters tend towards 'You can have it in any colour, sir, as long as it's brown' colour schemes, Serious Sam 2 is a welcome excursion into the other parts of the spectrum. It occasionally even goes too far. When moving through the Micro Machines style Tiny-tiny-Sam level which closed the second world, the riot of colours caused problems with losing the weird-ass flying witches in the undergrowth.
Which segues into another of Serious Sam's better qualities: the design of the enemies. Other developers work out grand design bibles where all characters come from a true imagined society, forming a neat fabric. Conversely, at least to these eyes, it appears Croteam doesn't care in the best possible way. If it thinks it'll work, it's in there. Models vary in actual quality of construction, but it ejects ideas like nothing else. The old favourites from the last game are all re-imagined - the bomb men now have actual bombs for heads, the bulls are enormous clockwork beasts - and intermixed with the new cast. These are either the most impossibly macho creatures you can ever imagine, or the most ludicrous, or both. Take the hulking American Footballers who charge and lob footballs at you, or, on the lighter side, the grotesquely fat clowns on unicycles presenting a uniquely bizarre appearance.
It's enormously silly and all the better for it.
However, just because there are a huge array of things to see and shoot in it, doesn't mean that it's not repetitive. It's not a game which anyone but the most slaughter-hungry can play for entire days at a time, and the largest encounters - which is pretty much all of them - are physically draining things. Serious Sam will tend to be something you boot up upon occasion rather than fall obsessively in love with. The co-operative play alone will mean that a true devotee of the death of imaginary people will have to return, if only to share a special, bloody moment with a friend.
But what drags Sam down is the pace-breaking additions, which in turn make it easier to notice its other faults. While the understanding of how to entertain someone in a game where there may as well be nothing but the fire key is huge steps beyond second-raters like the tedious Painkiller, it doesn't manage the consistency of Sam. There is a tendency in the level design to encourage Sam to be passive, pull back and let the monsters come to him rather than move through an environment and having them counter-attack. While the waves of enemies were always noticeable in Serious Sam, they're even more so in this one.
Serious Sam's still an enormously likeable game. Where games can be antiseptic, it's always clear that this is a game made by human beings with desires, tastes and things which they think are funny that no-one else has done. With the luxury of a budget, Croteam has tended to indulge a little too much in the latter and it's resulted in a less elegant game. But it's hard not to find at least some love for a game which thinks (for example) it's a good idea to put a crocodile in a Croatian jersey, hide it in a level and provide a CROcodile secret bonus.