There are a lot of clones and copies (CastleMiner, definitely! It's also a pretty terrible game...), but there are some real gems in there, as well.

Try playing Miner Dig Deep and not getting addicted! It's a really fun little game for the money, and I've found quite a few 8 bit indies that mimic other games (Breath of Death VII) which are pretty good. The problem with the indie market is that it's very easy to get a game into the system ("A Game About My Cat"...), so there will always be crap to wade through. It's just a matter of sifting through and finding the really good games rather than the bad ones.