The level design is pretty solid. If you are new to the series, you can choose newcomer but that holds your hand. if you played Mega Man before then play it on casual or normal. If you want a true challenge, play the superhero difficulty (which I just finished today).
The level design is again, pretty good but I recommend casual difficulty because in normal mode they don't give you much checkpoints. Not to mention that you might get some cheap hits here and there but once you learn and take your time, it's not bad.
The music? Oh man, it's ok but unless you pre ordered it, you will have to listen to the techno-ish music but if you like techno then be my guest. If you pre ordered it (like I did), you can change the music to instrumental which is easy on the ears. Again, that's only available if you pre ordered it. They might add it as paid DLC for the people who didn't pre order it.
Because I played the game about 3-4 times, I didn't notice any gameplay issues. I never noticed any lag or anything bad.
It's $30 which isn't too bad. You can probably beat it in 2 hours depending on how skilled you are. Like all Mega Man games, they have high replay value meaning that you can do buster only runs, no double gear, etc. You can also look at the gallery and play some optional challenges in the extras to keep you busy.
I recommend it to everyone! That includes the newbies to the series as well.