That's all it should be, a browser. Mozilla loads slower then snot (maybe this isn't an issue for those with 3ghz computers), and definitely does not parse HTML better then IE. Integraded mail client; uhm, yay? 3rd party e-mail clients are usually better and the web based mail my ISP provides works just fine. Integraded pop-up blocks; I don't visit porn sites so there isn't much need for that.
I don't have experience with Operah, so I can't say much about that. All I do know is that IE does its job and gives me no reason to download some other browser.