I love this game, alot. It completely blows the original out of the water. Here's some pros/cons:
Pros:
-More Playable characters.
-More Bosses
-More Items
-8 Billion seeded runs!
-Better mechanics
-A whole load of bug fixes.
-A massive amount of playtime.
-New Challenges
-Boss rush
-16 Endings!
-Easier to break >:) !


Cons:
-The Keeper..

In all seriousness, this is one of my favourite games of all time. Fantastic, active and passionate community, Northernlion's videos are what keeps me warm at night. Incredible fun, highly recommended.