I'm not against freemium games by any means - I'm actually just about to recommend you play one of them - but I do think there's something weird about the concept. It's weird that developers, who historically have spent most of their time thinking about how to engage players, have had to start pondering the best ways to frustrate them as well.
How to make audiences pay? That's the central design issue at the heart of too many freemium games, and as central design issues go, it's a hard one to love. How to annoy players just enough that they'll hand over some cash, but not too much that they'll give up on the whole thing? It's the hunt for the world's crappiest Goldilocks region.
Heroes Call's solution isn't particularly original, but I've certainly come across worse. For the most part, you'll simply be paying to cut down on the waiting times. Finish a quest in this likeably basic dungeon-crawler, and you'll be told you can't have a new one for, what, ten, twenty, thirty minutes? Don't worry, though, you can pay a few gems to get that quest right now, just as you can pay in gems to revive your character mid-way through a dungeon instead of heading back to the start of the level when you've been killed.