Actually i use Wizz air 6-7 times/year and I've found them to be fairly reliable. yes you should expect that your flight may leave 10-30 minutes late but they do a decent job of padding the printed schedules and you'll generally arrive within about 15 minutes regardless of the delay.

Your definately paying for going from point a to point b and thats it. And your correct that they generally don't bother worrying about weight with the exception of checked baggage (and in some locations they will charge you if over) and they now charge you to check bags. Since that change is relatively recent they may start to pay more attention to carryons.

Their schedule is interesting in that it contains a lot of very early flights and a lot of late flights (the late flights actually work out well if your travelling on business as it allows you to complete your day and still easily get to the airport - the early flights also are good in that you can arrive at your destination before 8am).

I always check to see if they flight a route if I'm travelling to/from Poland or Hungary from within Europe. Get a good fare and you'll be pleased with Wizz Air!!