#25 - Super Mario Galaxy 2 (Kudos to Player2 for guessing this)
Super Mario Galaxy was a revelation for me. This series of precision platformers suddenly blasted off into outer space and had all kinds of weird and wacky Ratchet-esque gravity mechanics added, while keeping the brilliant jump 'n' run gameplay and traditional Mario aesthetic. Add in some collectathon exploring like I loved from the 5th gen, and you have yourself a classic.
In many ways, SMG2 is much better than the original. But, in other ways it's a lot worse too. It did feel a little like an expansion pack rather than a new game; and I didn't take to Lubba and his ship the same way I took to Rosalina and her story.
However, level design was a bit step up from the original; Yoshi was a nice new addition and as much as it felt like a cash grab, I was actually happy to have my cash grabbed by it. I loved everything about the original SMG, so I happily paid to have more of that. I hope this isn't the last we've seen of the 'galaxy' sub-series because I would happily pay even more again to have a crack at exploring some new levels with Mario at the helm.