Definitely worth playing, IF you played the first game.
The general feel of the game is similar to the last; beautiful 2D platform with 3D effects, the colors are amazing. The environments are very lush and the animations are fluid. The music is also very good, which is a very critical aspect for me. Same composer from Rearmed, but this time he had to be a bit more creative by writing his own melodies. The original tracks are excellent, but I'd say the new remixes are just good but not great. Still I'm looking forward to getting the soundtrack.
One thing slightly different from the first game is the bionic arm mechanics. The feel of swinging from platform to platform has the feeling of nostalgia, bringing me back to how much I loved the first game. However, some things have been changed, some for the better and some that just make the game frustrating at times.
The good: While swinging, you have plenty of control of where to go once you have latched on to something. You can start swinging from a dead hang, or you can reel yourself in and out giving yourself a lot of freedom. Another change is you can shoot the arm at a diagonal while moving forward. I find this feature makes it easier to keep moving forward. Now, because you can do that, you no longer can shoot the arm straight forward standing up, so it's a trade-off.. which leads me to the bad.
The bad: I have no clue why they made the arm button the same button as the release button.. The same button shoots the arm, pulls you up a ledge, or let's you go. This is extremely frustrating when you're swinging trying to pull yourself up, and you hit the button and instead of being pulled up or climbing onto a ledge, you fall into a lake, or spikes below! The jump button (getting into that later) also releases the arm.. why not just leave that button as the only button that releases the arm, so you don't keep detaching by accident?
Unlike in Rearmed, the swinging itself feels different. It used to feel so smooth but now feels choppy and forced. It feels like the physics are all messed up. You can't do any cool release tricks like in the previous game either. Even if you reach the end of your swing and start to move the opposite way and release, you still end up traveling in the 1st direction, which obviously defies momentum. That, and you stop swinging if you don't hold the directional button, which is fine but you stop abruptly and it doesn't feel right.
The new jump feature: I'll argue that the jump feature is exactly what it should be. It's inaccurate, short, and generally not too important. If Spencer, or anyone else with that kind of artillery on their arm could jump, that's about as high as they would get! It'd be stupid to have him jump 3 times his height, he doesn't have bionic legs! You also don't need to use jump at all in the game, and there's a retro difficulty after you complete the game that disables jump anyways, so anyone who doesn't like it doesn't even have to worry about hitting it on accident.
The weapons: The default pistol is pretty much the same thing you got in #1, and you'll find an improved shotgun, but there's where the similarities end. Every time I got a new weapon I thought it was useless and stupid, until I figured out how to use it. For example I thought that magnet thrower was the stupidest thing ever until 8 hours later when I finally figured out what it was designed for. You can shoot it straight and it comes back to you, so if you shoot it and wait for it to reach it's maximum distance you can duck, causing the element to follow you, so you can shoot it over barrels and nail guys in the back who are hiding behind them. Kinda neat.
It's fun to blow things up with the new bazooka, but Rearmed 1's bazooka is far superior. You can't direct it, just lock on and fire. There's also the napalm gun that's just as dangerous to you as it is to anyone else. Get caught in it's blaze and you're dead. Lastly there's this electrical weapon that fires a ground walking energy ball that can be used to activate switches, kill soldiers, or mess with mechanical enemies.
Sub weapons and other equipment: I don't want to get into all the options here, just want to point out that it is annoying that you can only use one upgrade at a time, and when you need to change you have to go into a menu, select what you want and return to the game. The menu screen does look really cool though, as Spencer rises from a circle of light in the ground showing off his equipment.
I played the single player through and it did take a while. It's a good enough time to get what you want out of the game. It isn't too long or too short. You can always revisit other areas instantly unlike in Rearmed, which is nice, but also not as challenging. No more are the roaming map enemies that you have to either avoid or encounter.
The dialogue isn't as good either. There are a couple of good lines in there, but it feels a little rushed. Also the dialogue screens advance automatically, and pretty fast too. You have to read it quick if you want to get everything.
Well I think this is long enough already, so in short, play it if you liked Rearmed, but if you didn't, get the first game and see if you like that first because it's definitely better.