The thing with playing roulette is that you are pitting 2 laws against each other.
1. is the law of averages, which is exploitable by being patient and having a reasonable betting system, BUT
2. each individual spin of the wheel is not influenced at all by any previous spin, so for each individual spin, the odds are the same of the same thing happening
for example, the law of averages says that if red came up 5 times in a rows, black is overdue to come up, but the next spin of the wheel still only has a 18 out of 37 chance of being black (less than 50%, because of the 0), regardless of what the law of averages says. If you keep betting black, eventually you will win, but theoretically you might need an infinite bankroll to keep upping the bet so that you'll recover all your losses if black doesn't come up for a long time.
I just tried one of those roulette systems last night, won $100 lost $100 won it back and lost it again, with the problem being that winning takes time, losing is very very fast. What I've learned is: don't be greedy, set a target where you are going to stop and walk away with your winnings. And on the downside, set a stop loss for yourself, so say if one set of bets have lost you more than $25, walk away and try again later.