Just finished RE2 three weeks ago, then bought and started playing RE0 two weeks ago, and last night I dusted off my copy of RE and started playing that as Chris.
Of the three RE2 was definitely the easiest. I thought that RE0 was hard at first, but once I actually got into the mansion things began to get easier, and by the time I got to the end it was no problem. RE1 on the other hand is just plain nasty with Chris, zombies can take up to 9 bullets to drop, and at the beginning, ammo is scarce scarce scarce...
OK, back to RE0. I was able to finish it my third time through with an 'A' rank and a clear time of 3 hrs 35 min (5 minutes over! Damn) on Normal
Here are a couple of RE0 pointers:
-Billy can take waaay more damage than Rebecca, so always make him your default character. If there's a room with monsters that attack you right away, have Billy go in alone first so that Rebecca doesn't get greased right off the bat
-otherwise, always go everywhere together. Two guns are better than one, especially when dealing with plain old zombies
-there is more than enough ammo and health to see you through the game on the Normal setting
-don't use anything on the zombies except for the pistol. On one or two occasions you start off in a room with a zombie right beside you- that's the only time when you should use the shotgun (aim up and blow off the zombies' heads with one shot). Stab zombies when they're on the ground to save bullets
-likewise, save the magnum for the boss (bosses, heh). Don't waste it on the Hunters, Spiders &tc. Those are what the grenade launcher and shotgun are for
-the shotgun works best on the Eliminators (the apes). These things are fast, so you need something with a wide spray. The shotgun will almost always hit, but there's a really good chance of missing with the grenade launcher, and the handgun doesn't do enough damage
-in order to save space, once you get the more powerful weapons, only carry around one handgun (the modified one, if you can find the extra handgun parts). Give it to Rebecca, and let Billy have all the heavy weaponry. You won't even need two handguns in the Water Treatment Facility
-most rooms only allow you to drop five or six objects, so try and organize where you keep everything. Create a 'health object' room, and a 'gun and ammo' room. Keep these rooms central, so it's easy to get back to them. The main hallway of the mansion is a good example. The second floor conference room, or the first floor dining room are also good places to store stuff
-don't bother to carry around ink cartridges. Unlike other RE games, all of the typewriters have an ink cartridge located beside them
-you don't need the grappling hook after the first Cable Car room in the Lab under the Church, so once you've used it there, you can ditch it to save space. You only use the thing four times in fact: in the train, in the church, to get to the second floor of the Lab, and to get to the second floor of the Cable Car room
-whenever you see a person-sized red or green gas tank (I don't know what these things are called in the English version) have Rebecca fill up her medicine pack. You will need a combination of the red and green medicine twice during the game, so keep your medicine pack stocked every chance you get. You can use these tanks an unlimited number of times, so keep filling up at the same ones. There's a green one in the Mansion in the Infirmary, a green and red one in the Lab under the Church, and a green and red one in the Water Treatment Facility. The only ones you really need to use are the ones in the Lab though, just make sure that Rebecca does the second floor and not Billy
Umm, that's all I can think of for now. I'll be back later with some 'Leech Hunter' pointers.