The biggest issue I've had with 3rd party apps is rarely the phone will freeze, but turning it off and then back on always works. Its happened maybe 5 times in the month since I've had 3rd party apps.
Have to say though, besides being fun to try new apps that come out, the only ones I like are nes, labyrinth, and customize(to change stock images around). Might be adding the gas app(finds the cheapest station for you) and the money app(tracks your spending(waste to much on crap lol)