This modular adaptability will lie at the heart of the game, and it's the thing that Perpetuum is going to share most closely with EVE. Finding the right loadout for your chosen ride is going be crucial to your effectiveness in the field, and being useful solo will mean quite different things to being useful in player-versus-player, or in a group. What's great about that is that you'll eventually be able to field a whole hangar full of bots, each suited to different tasks.
Once out on the planet's surface you are faced with a weird alien landscape full of plants, mountains, more techno-fortress things, and other robots. There are a whole bunch of NPC robots that you can shoot up for resources, and these rapidly get dangerously tough as you wander off into the surrounding areas. Some are simply hanging out, waiting to be exploded, while others are tied to the various mission objectives you'll be able to take on. (The missions right now seem ludicrously tough, but I guess that's because I've tried to solo them in a crap robot.)
What's sort of interesting about this early wandering is that you get to see how Perpetuum's terrain-based interactions affect things. You can't hide in the depths of space here, and there's real scope for wandering into danger, either from NPCs or other player robots. Combat here is handled in real time - you move your robot around with the WASD keys - but firing and damage is calculated per turret, or per missile launcher. Whether you hit, and how much damage you do, is a factor of your skills, the type of weapon, and the range you choose to engage at. PvP is, of course, fairly open, and it feels a lot like EVE. I've yet to see a proper pitched battle, but I should imagine it's going to be fairly intense (and fairly laggy) when two sides manage to pitch two armies of robots against each other.
Perpetuum is currently in closed beta, with waves of invites being sent out to grow the population as new features are implemented. Most recently the game introduced a mission system, which perhaps gives you some idea about just what a sandbox it has been up to now. The world prior to missions could simply be explored, with the options being to shoot NPCs or mine for material resources. Getting a player-driven economy up and running is clearly more of a priority for these developers than creating the kind of quest-driven systems that are the motor in other MMOs. That's a good sign, because it means they've got their priorities for how the game should work just right.
It's not clear right now when this game will launch, or enter any kind of commercial phase. Avatar Creations have announced that they're "looking for partners", which is emblazoned on the game launcher itself. The technical hurdles to getting such a game online for a large audience are not inconsiderable and could end up being Perpetuum's greatest challenge. You can keep an eye on things over at the official website.