A few things:
1. MH3U on a 1080p screen
2. Different character than in 4U (HH in 3U, IG in 4G)
3. Controller
4. Barioth, Nargacuga, Qurupeco, Gigginox--some of my favorite monsters to fight that aren't in 4G
I just got so into it again that I stopped playing MH4G for a while. I still love MH4G, naturally.
And as for your last point, that's kind of a limiting mindset. Spice things up and try a new weapon or something! It's natural to prefer a weapon and be curious about what changed, of course, but I would suggest trying something new. I can't tell you how to play, though.
The thing about MH is that even though you do almost the same thing in every entry, they still make it fun with enough slight differences. Heck, I'm already back to the HH after not using it in 4G and appreciating the slight changes to the note system.