Not sure what the first was. Probably Summoner on PS2. Not a particularly bad game but not what I was expecting either.
Other than that, most games on the Wii that tried to cater for the core, non-Nintendo audience. The Conduit, CoD3, Cursed Mountain etc. They all had issues ranging from awkward controls, poor optimisation or just bland game design.
Biggest regretted purchase though has to be Final Fantasy XIII.