Well there are definetly good games on the 3DS you should check out.
First if you are interrested in Pokemon, you can buy either X/Y if you want something new or OR/AS if you want to play online, as most Mega Evolutions in there are not present in XY.
There are some Sonic games too, but I'd have to say they're not really that good;
Sonic Generations... well act 1 and 2 look exactly the same in term of gameplay once you'll beat the first boss.
Sonic Lost World... Actually the best out of the three, it's pretty good even tough the level design is pretty linear compared the wiiU version.
Sonic Boom... Haven't played it but the demo, but it's actually better than the wiiU version, apparently.
And finally, 3D Sonic1 is just Sonic 1, as I heard. It still runs better than it did back on the GBA ;P
Now the console itself is not really that expansive, but if you plan on buying one, I'd suggest immediatly going for a New3DS, this will avoid you having to buy one after N3DS exclusive games come out. I saw a N3DS around 170€, don't exactly know what it makes in $ tough.