Huge disappointment for me I'm afraid. It was a valiant effort, but in the end this game hasn't got enough variety to keep me interested in if for more than a few minutes at a time.
Making the series more open ended was a wise move, but it falls short of the mark due to some severe problems. In the process of making the game 3D, the graphics have suffered as a result. Textures look ugly up close, and so do the character models. Controls are fine, apart from the fiddly aiming at times. Unfortunately you'll be doing the same thing over and over again throughout the game, with very little difference each time.
Overall, it's by no means a bad game. It can be fun at times, especially when you get your hands on a new weapon. It's a shame that there wasn't enough polish though, because this game would've been much better if it had been tweaked just a little bit more.