I kinda really love MM10, like, a lot.
In fact, shamelessly plugging here, I wrote the one and only walkthrough for the game (as far as I know) on the internet. I just... really love it!
I think it's overall about as good as, if not slightly better than, 9; MM2, 3, 9, and 10 are all the "crown jewels" of the classic Mega Man franchise, in my opinion. 9 has more classic nostalgia what with the sounds and songs ripped straight from Mega Man 2 and the style of the music and everything much more classic, whereas 10 has a bit more flair; a lot of people hate move the music at first but grow into it--a lot of it doesn't sound that Mega Man-like but in fact each boss's theme was composed by a different composer from the classic Mega Man games. And of course you have all the difficulties and two characters from the get-go, with even more and more modes as DLC to keep you playing. It's great, really fun, lots to do, and a good challenge. Less cheaply challenging than 9's plethora of instant-death traps and it's much cheaper and easier to buy loads of Beat Calls and Shock Guards to keep yourself form dying in 1 hit anywhere in 10,, but the outright challenge of enemies and bosses mixed with less overpowered Master Weapons than 9 means that it's got more *fair* challenge.
And yes, Bass DLC is worth it. I'd say all 3 special stages and Bass are the best DLC for the game.