Finished it.
Mini-review below.
The game's length is similar to the first one's (it may even be shorter if You skip the optional content), but that is actually good, as the gameplay (fistfights! and more fistfights!) would not be able to sustain more hours. Also, I prefer the quality of content over quantity, and quality is definitely there.
I still think that the move from Source to UE3 was not a very good one, and the auto-healing after death&respawn is a lame hand-holder system, but other than that, the game is good. The setting is as bizarre as expected, or even moreso, with the art style wonderfully weird and the voice-acting equally zenoclashy as previously.
Open world does not add much to the game, except allowing (or even requiring) backtracking, which is nice from "get all collectibles" point of view. And you need these for some side-quests (yes, there are side-quests), although gathering of the three type of collectibles has very uneven pacing. The first part of "collect butterflies" side-quest can be easily resolved around 1/5 into the game and it nets you the best reward: endlessly respawning weapon supply. On the other hand there are only 8 cubes in the world, they can be easily missed, and - You guessed it - You need all of them to [spoiler deleted].
RPG elements are largely superficial and are there more to customize your character rather than develop it (hint: RPGs require you to develop your character [hi, Nameless One], while RPG wannabes allow You to customize him/her [hi, ME2/3-Shepard]) and if You want a more challenging game You may want to skip this completely. If not, You can increase Your Strength (more damage), Health (more life), Stamina (more punching until *pant* *pant*) and Leadership (can recruit stronger allies). For example, I maxed out my Leadership and halfway into the game recruited an ally who almost single-handedly destroyed most opponents from that point on, except the end boss. You can only call allies for specific battles, so in hindsight investing in other stats is probably more efficient (and more satisfying).
TL;DR & summary: If You liked the first one, You should like this one too, but I wouldn't pay $20 for it. Wait for a 50% off, or something.