The memory limits will definitely completely prevent you from running some real-world programs. Programs that don't fold well into a single threaded event loop are also a problem at the moment (including Unreal/Unity games that use background threads).

Also, unless you definition of "can run a game" includes "can run a game at 3fps" I'm pretty skeptical that the entire repitoire of games for those engines can make the jump to WebAssembly today.