Yes. It feels heavier, but stock for stock, it would've beaten my car in nearly any handling situation. The ride quality is better. The build quality is better. The sound system is 1000x better. Comparing to pre-09 e9x's, the controls are much more easily accessed. It has a better stance on the road. It looks like a higher end car. And it sounds amazing. I love my 335i to death. But I would never be as fanboyish to think its a better car than the S5. It just doesn't feel like it's on the same level.
And it really doesn't drive like a buick. Via
http://www.fastestlaps.com/index.php?page_id=compare&car1=45fd0fcbd70cb&car2=458da72e81532
Nordschleife S5 - 8:26 335i - 8:26
Hockenheim Short S5 - 1:17.2 335i - 1:17.8
Autozeitung test track S5 - 1:44.6 335i - 1:45.8
SportAuto wet handling test S5 - 1:29.8 335i - 1:35.8
Serres Racing Circuit S5 - 1:34.80 335i - 1:35.25
Hmmm, so its as fast on the the ring, and slightly faster everywhere else... even though its a lot heavier. Sure it doesn't feel as agile and as quick. But results are results. Just ask the GTR about "results" even when its handicapped by weight and the un-bmw-esque AWD. The S5 does all of this with vastly superior ride quality to the OEM crap that comes standard on the 335i that so many on this board have tossed for something aftermarket.
You know, someone on here has a quote in their sig from a G37 vs. 335i comparison in which a writer said "I'm not sure what it is, but the 335i feels $15000 better" or something to that extent. If you spend one night out in an S5, you'll say to yourself "I'm not sure what it is, but the S5 feels $15000 better." And if you don't you're probably better suited to driving a Z4, S2000, E46 M3 or something else that actually comes as a performance car. The S5 is absolutely fantastic.
I do love my 335i to death though. I wouldn't trade it in right now for anything not named 911... but that's $12000 in mods later. Stock, I really wasn't that impressed. The S5 in stock configuration; however, is damn near perfect (near = supercharger

)