How it compares to 3U? I wonder if its worth picking up if I have already previous game on Wii U.
It's better. Few niggling issues for me though.
Monsters seem to have less health over all, whereas breakpoints seem to have more HP overall, this is just from observation though. Normally with an Iron Grace it took me about 4-6 minutes of fighting to beat it in 3u and I could break the frill consistently within about 2. Now the frill either breaks right before I kill it, or doesn't. And the kill takes 3-5 minutes in general. I decided to time myself while trying to get a kings frill for the Jaggi set waist.
Beyond that, you are more mobile, which means there's more ways to avoid the enemy, which on one hand, adds depth to the combat, on the otherhand, I see no reason to use block weapons anymore. Because, I am normally mobile enough to avoid most attacks from the enemy.
Combat with some monsters, like the flying monkey anteater lemur, have easy cheesy solutions. Namely exploiting the jumping system, and knocking it down repeatedly. I defeated it purely using jump attacks at one point. Just by running and jumping off the nests at it.
Some of the monster's element types don't make any sense. Why is the flying monkey anteater lemur, a water attack using creature? That's like saying a Llama is a water based animal because it spits. In MH3U most of this stuff made sense. The monsters also looked the part. I was expecting the Kecha to click it's ears and spit fire the entire time when I first spotted it. Or be poisonous. Or to throw dirt at me, it wasn't until the second time, when I got hit by the spit that I realized that it had water based attacks.
But the pro's definitely outweigh the cons.
The mobility you have, makes the game FEEL better to play. You're reactions are just sluggish enough to be realistic, without being quick enough to make you think you're a Souls protagonist.
The monster's have a better variety, so some illogical ones are to be expected.