Its a ok price for one and you got two of the main good games on it.
What you need most of all is a rechargeable battery pack.
The Game Gear drains battery's in about a hour. It can be played off the mains via a Mega Drive (not 2) power pack.
Games wise I link to this nice site
You can get a Master System converter for it to play them games on the go, but be warned games with loads of text are hard to play via that (Ultima IV is a big offender)
The TV tuner is ok. For the time it was great. These days its a bit arsey (and don't work in the UK anymore), but one handy little thing is you can make a areal lead for it so you can connect anything that uses the aerial socket on it