Another way to kill him (without the rocket launcher) is to stab the "crystal" in his chest. How do you stab it? It's really easy, once you know that you CAN.

After all the annoying button mashing and boulder rolling, you and SHEVA need to bail to the upper area of the map. Wesker should be behind you. As long as you are NOT in the final showdown area, Wesker will only do that uber-cheap, weird whipping attack with his arm (the one that knocks you into the volcano if it touchs you).

Once you get to the top, the actual fight will begin. Wesker will start doing attacks that you can dodge (except for his other instant-kill: the tentacle tornado). When the crystal is visible from his chest, (and you are CHRIS) run behind him and shoot him in the back, so that he stumbles, then run up and jump on his back like a rabid monkey. Enjoy the final button mashing sequence and ending cutscene.

If you are playing as SHEVA, shoot Wesker in the knees when the crystal is in his chest so that he stumbles. CHRIS will automatically run behind him and grab Wesker for you.

In my experience, it MUST BE CHRIS that grabs Wesker from behind. Sheva doesn't seem to put two and two together. Which isn't suprising, considering how many times she has to ask Chris if Jill really was his partner.

Enjoy. Don't forget to pull the triggers in the final cutscene. =D

Ok... It's really expletively frustrating if you don't know how... Heres what I did... When everyone starts in the middle, turn around and wait to jump down. I waited for Sheva to fire on him. There will be a cutscene of Wesker. Jump down and wait till he jumps down and run back up the hill turn, left and wait for wesker to start walking up the little hill meanwhile taking a few shots... then run where you jump down and wait... another cutscene happens showing weskers heart. Use an RPG on it and your done! I just did this in this order and thats how I beat it. Hope it helps!

There is a trick, you need to pull off the big red GAS tanks onto the floor, when the monster walks over it, hes going to absorb it, and thats when y ou shoot it, hitting his weak spot for MASSIVE DAMAGE!

Weapons I recommend: 1 RPG, Sniper rifle(rapid fire), shot gun and some healing.When you first exit the cut scene with Wesker, turn around and run to the rock bridge. You will enter another cut scene. After this ends you should be facing a small gap across from an island, with Wesker behind you and Jill above you. Jump across and run to the top of the island and go to the ledge to look down at Wesker. Jill should be shooting him and she should hit his sweet spot. I joined in the fun too! There's a cut scene and Wesker jumps to Jill. At this time equip your sniper rifle and wait until the cut scene where Jill almost falls down off the bridge. When this cut scene ends, you will need to shot Wesker until Jill is safe. When she is safe, be prepared to dodge 2 attacks from Wesker, then head to the boulder on the lower part of the island and follow the prompts. When the boulder falls and Jill crosses over safely to your side, head to the top of the island again. When Wesker appears and cut scene ends, open fire with the shoot gun and dodge(if needed). When the yellow puss appears on him, equip the rocket launcher and hit it!! He's a goner after that. Be prepared in the ending to hit the "R and L" buttons to completely end the sequence. NOTE: I did this on NORMAL difficulty it may vary at other levels!