OK as someone who played most of Monster Hunter 3 Ultimate (never finished completely as I hated the underwater battles) and then put 200+ hours into Monster Hunter 4 Ultimate (yeah finished the key quests, and it was fun!), I must say Monster Hunter Generations is a step up in fun! For people who have played any of the previous few MH games, MHG will immediately feel familiar given the 100s of hours of training the hands to hunt monsters on the 3DS! So I didn't find issue in the seemingly slow starting couple of hours (and this is important for the benefit of newer players) - because I knew what was coming was going to be fun. And fun it is!
I'm now nearly 200 hours into it (mostly spent hunting online with hunters around the world!), and all the fun elements from MH4U are there - but it's the additional stuff that makes MHG the superior one, and I'll name a few:
+ Hold A button to keep gathering (in the previous installments, you have to keep tapping A, getting RSI)
+ Hunter Arts is a fun additional moves that builds up a gauge over time to execute a strong move
+ Hunter Styles mean no matter what weapon you have, you can jump over monsters! (no longer need to envy those fun jumping Insect Glaive hunters!)
+ Play as a Palico - yeah the cat! As a cat, you have 9 lives instead of 3, you have unlimited stamina, etc... so fun...!
If you've played any MH in the past, you'll just slip comfortably back into it. If you're new to MH, this is as good a time to join in the fun (plow through the first couple of hours, and the world will open up!). And of course, the best aspect to this game is being able to hunt some of those monsters with 3 other hunters - wherever they are in the world!
Love it and highly recommended!