i've been working on a game, and i use realm crafter. it's pretty simple, and it has its own little editors, that range form making terrains to making rocks. =p
and if you're sorta serious about making a game, realm crafter's price doesn't seem as much if you see some other 'spensive programs
not well on a crappy computer, unless you like waiting at the map loading screen, and by the time you join the match, you notice your team needs 5 more kills to win.