FarCry Instincts Evolution is just a continuation of FarCry Instincts. Only get it if you enjoyed FarCry Instincts.
The graphics are virtually the same as in FarCry Instincts, but there are a few points in the game where you are more likely to notice the flat-sided trees, and you'll notice that the character models do not look all that great up close. The environments are wonderful, and most are full of great looking vegetation. So the graphics are good, but the shortcomings of the graphics will be highlighted at a few select points in the game.
The sound is generally good, and is basically the same as in FarCry Instincts. However, using a scope or binoculars simultaneously amplifies the sound of whatever is being viewed. It seems like that should have been caught and fixed before the release. Late in the game, there was an audio clip of a bunch of people yelling in the distance that would play every time I loaded a save point, and despite loading several different save points, that clip always played. I don't know if it was meant to do that, or if I hit a save point during a sound clip causing the game to glitch that clip into all of my saves. Either way, it was odd but not annoying. There were also a few places where the sound cut out entirely. The only time this was really a nuisance was during a cutscene with the final boss... it kinda sucks when you miss out on one of the few places where the story is being developed and explained. The music and sound effects were great and added a lot to the mood of the game. So the sound was good overall, but it still needs some polishing to be as good as it was in FarCry Instincts.
The gameplay was generally excellent. The game has the same basic controls as FarCry Instincts, and Carver starts with the abilities he had at the end of FarCry Instincts. There was a noticeable improvement made on the feral jumping and being able to control it. In FarCry Instincts, the feral jumping was fairly limited to running leaps and was almost useless for vertical jumps, but FarCry Instincts Evolution allows for purely vertical jumps as well. The game has a much more open feeling than FarCry Instincts, and the levels of FarCry Instincts Evolution will occasionally require just a bit more use of the feral jump than its predecessor. The added jumping is often just to give a second approach to an objective, but sometimes it is required, and it was generally an enjoyable addition to the game. So this game is definitely enjoyable, but there are some points of the gameplay that I did not like. The most annoying part of the game was getting stuck at the top of a climbable wall or vine. Those things apparently have a bad tendency to wrap around Carver's feet to keep him from going anywhere. I was slightly disappointed in the final boss fight since I had a harder time getting to that fight than winning that fight. There were also the same problems with the AI spotting me through the brush that FarCry Instincts had. On occasion, stealth was possible, but it was generally much simpler and more reliable to just run into a group of guys and slash them up. So the gameplay was generally great with a few areas that needed to be polished.
The story is lacking. The developers had to come up with something fairly odd just to keep the story set in the same kind of tropical environment that they worked so hard to develop and to set you against enemies of comparable abilities. So there is a little bit of a story, but it doesn't have much detail, and it seems to be a bit of a stretch. The character relations and dialogue were never enough to draw me into the story or make me care about what was happening.
The map editor has been improved a bit since FarCry Instincts, and it now has more objects (including mounted gun and rocket turrets, zip lines, tunnels [fairly low quality, but tunnels none the less], and a new boat. I'm sure there are other improvements as well, but I've only spent a couple hours creating a map, and I have no internet, so I can not seriously comment on the multiplayer aspects of the game.
Basically, FarCry Instincts Evolution is definitely fun to play. It fits nicely into the FarCry franchise, but with a bit more effort put into polishing the final game, it could have been great. The flaws that it does have make it seem like the game was rushed in order to just make a bit more money off the FarCry name before moving on to something else. So I recommend FarCry Instincts Evolution only if you have already played FarCry Instincts and loved it. Be prepared for a few minor disappointments that pretty well offset the improvements, but also be prepared to continue the Jack Carver experience for another several hours as you play through the campaign.