Nothing really pertaining to do with the main story, but if you hit dying status with Barry Burton in the Mercenaries Reunion, you'll bear witness to the poor guy yelling "Don't let me die!" At first this seems nothing more than a dying plea, but if you're a hardcore Resident Evil fan then you will know Barry has a wife and two daughters so in essence he's begging you to save him from leaving his wife a widow and his daughters fatherless!
If it makes you feel better, keep in mind that Resident Evil 5 is set about 10 years after the Mansion Incident. Barry's daughters are more than likely college-aged by now.
It seems that overdose of his own serum just made Wesker... drunk. He doesn't lose his speed nor strength nor healing, but with each shot he staggers more when walking, he gets a headache, his vision blurs and his ears start ringing, and there's a drastic change in his behavior and speech. After the first dose of serum, he completely loses his usual cool, becomes loud, angrily raising his voice at Chris (rare for him), spits some God complex bullshit, and is easily beaten by Sheva. After the second... well, he does such things that he'd never do if sober, but would be prone to if drunk, such as shouting "comic book villain's ideas", completely forgetting that Chris & Co eat superstrong monsters for supper, while the superfast Wesker has teased them for years, and the whole "Look, Chris, I just turned my arms into awful Combat Tentaclespermanently so we can fight like men, isn't it cool?" thing. And his final Taking You with Me, while he could reach a rock and pull himself from lava much easier.
Wesker's final form has been said to be a bit of a Clipped Wing Angel; he's got exposed weak points, is no longer as fast, and can be defeated by repeated stabbing. Worth noting, however, is the fact the final battle takes place in a volcano; the earlier Uroboros you fought displayed an aversion to heat (the first being killed in a furnace and the second being particularly vulnerable to flamethrowers). He's in the absolute worst environment he could've been in to expose himself to Uroboros. Still, granting him an out on this ground doesn't excuse the fact that Sheva and Chris didn't immediately burst into flames, but still.