In RIP 1, you are a turret. You can't move, and you are usually located in the center of a small map. Enemies come at you from all directions, most of the time in groups and in formation, and attack you. That's it. There is nothing else to the game. Looking at the screenshots you may think, “this looks like it was made in the early 90s even though it was released in 2007.” You may be right, but it does manage to be mildly fun. As you progress through the 40 levels, you will unlock perks, and there are also about five or so weapons available to you in each level. Sometimes you will have access to three or four of these weapons, and you may choose which one you will use. By trial and error you will figure out that depending on the level, some weapons are much better than others. It took me about one hour to beat the game, and I would say that it was a decent hour of simple, yet fun top down horde shooter action. There is no reason to play through it again, but what it provided in that hour was enough.
RIP 2 - Strike Back:
RIP 2 takes your character of choice out of the turret and makes the game much more twin-stick-shooter-like. With that said, there are still a few levels that require you to use the turret, and they have also added two vehicles you could use in several levels. There is a tank and a cumbersome helicopter. In addition to the vehicles and new control mechanics, the developers also added some new enemies and a few bosses scattered throughout the 60 levels. RIP 2 is noticeably more difficult than the first game in the series, but it's still manageable with the exception of having to repeat one or two levels several times in order to beat them. The enemy pathfinding problems are still there, and because some levels have many more obstacles than on the first game, it becomes much more obvious to notice that the game's AI leaves much to be desired. RIP 2 is basically 60 more levels of the original game with the addition of a few things here and there. It's virtually the same game, but with more levels and some new mechanics. With that said, it's comparable in enjoyment to RIP 1.
RIP 3 - The Last Hero:
This is the first game in the series to actually make an attempt at fleshing out the story. This adds nothing to the quality of the game, even though some of the cutscene artwork is decent if you like their 90s style. The AI and pathfinding problems are much more noticeable in RIP 3 than in the two previous games. This has more to do with the level design being generally worse than in the other two games. Strangely enough, even though it may seem like the developers spent more time with this third installment by adding a few more interesting weapons and polishing the graphics and overall presentation a bit, the game suffers technically, as the AI's behavior is erratic at best, and extremely boring at its worst. Not much has been done to make it better than the other games. It's as if the development team had the urge to make the third game, but very little interest in attempting to make it better. RIP 3 is the least enjoyable of the three games, as it steps down in quality quite frequently through the 100 levels.
The other reviews of RIP - Trilogy are quite harsh. I agree that these games aren't good, but the amount of negativity seems to be coming from people who didn't even give it a chance. If you like simplistic, retro style arcade action, this package is at an OK price and will provide you with a few hours of fun.
RIP - Trilogy is okay.