Bonk, the wackiness thrills me.  The character design, charm, the music & sound effects in the first 2 games.  Spinning, bonking, the giant bosses.....& the music, did I mention the music?
As for Bravoman, I'm happy I bought that game all those years ago, love that game.  True, I use the cheats, but, always loved that game.  Impossamole is an acquired taste, to be sure.  Hated that damn game the night we rode our bikes back from Toys R Us when it came out.  Then, after soaking in the pool for awhile, my buddy & I cooled off, & decided to give it another chance.  That game has cool characters & flipping awesome music.  It's a seriously flawed game, but, I enjoy it.  And quite frankly, it's probably the best of the entire Monty Mole series, though, I can't say for sure.  I've only really played the Amiga version of Impossamole....