Hybrids are funny like that so you're not the only one. But I generally classify them in 3 categories.
Mini woods - The majority of hybrids out there. Head just looks like a smaller version of a fairway wood. They have more sole camber like woods, little to no offset. (RBZ, Superfast, JPX825, Xhot, Anser, ..etc) These are for those looking to replace their fairway woods with something shorter and easier to hit, typically you'd swing these much like you would with a fw. Much like a fw, they do best in a better lie scenario.
Driving irons - (H4, 712U) Less common and usually for players who already hit their long irons fairly well but would like something more forgiving or a bit easier to get more air on them. They just look like a bulkier version of an iron, flatter soles, little bit of offset..etc. Usually the same or only 1/2" longer than its iron counterpart. You swing these much like an iron, slightly steeper approach, hitting down on it a bit more than you would with a "mini wood".
Utility Hybrids - (G20, Super 9031, original TM rescues) These have face much like an iron with a slight bulge in the back like a wood. These types are more utility than anything. Mid to higher cappers tend to benefit from these because its a very in the middle of the road type of club. They also work fairly well out of light rough. Variations in swings like if they sweep it too much or hit down on them too steep, it stays rather forgiving and keeps the ball out of serious trouble.
Ofcourse these lines are very blurred but when looking for a hybrid, I think the first thing you want to ask yourself is what you are trying to replace. Are you looking for an easier to hit woods for those long approach shots, or are you a descent irons player looking for a slight edge, or a little bit of both with something that can be your long range club to get you out of trouble.