First off, I just want to say I love this car. Compared to my previous "sport" compact, a 2001 Cavalier Z24, this thing is a dream. The Z24 is OK for someone who is just starting to work on performance driving in an econo-sport, but this car really takes it to the next level and beyond.
Power delivery is strong right off the bat - almost too strong. Torque steer can be an issue, but just be aware of it and you will begin to appreciate the fact that you have plenty of power to work with. The QR25 is an excellent engine and pulls strong right up to 6200 RPM. It may seem like overkill to use such a "large" 4 cylinder, but keep in mind that despite the larger displacement, this engine is actually smaller and lighter than the previous 2.0L engine (the SR20) which is so highly regarded in the sports compact community, and makes significantly more naturally aspirated horsepower (175 vs 140). With some work, you can easily make 200 N/A hp out of this engine. If you want turbo power, I have seen talk of early turbo kits that produce almost 270hp at 8psi (SRT-what?). From what I have read, this engine will probably not handle over 350 without extensive internal work.
The 6 speed transmission is great, a significant improvement from the 2002 model (from what I've been told). It shifts well and has a solid feel when going into gear. Occasionally when cold it will feel a bit stiff, but once warmed up it is fine. In 6th gear, the car runs at about 3100 RPM at 80 mph, which is fine. This car is drag-limited at about 135mpg from what I hear. I've only had it up to 120 (off-road, of course ;) but felt like I had plenty of room to go. The only problem is getting it into reverse if the car has been sitting; sometimes it won't go all the way into gear, but either putting it into a forward gear first or letting the car roll a little will fix this little problem every time.
This car handles extremely well for an economy sedan platform. The suspension is fairly stiff, but not to the point of being uncomfortable; just slow down for those speed bumps. Steering is nice and responsive, with a good feel for the road. The wheels, though they look nice, are unnecessarily bulky at a hefty 24 lbs. If you want to squeeze every bit of performance out of this thing, consider lightweight aftermarket wheels. The Continental tires are fine for most spirited driving on the road (these tires even come stock on BMWs and Porsches), but like most street tires they will break loose if pushed hard (I was all over the place while autocrossing on them). I will most likely go with a different brand when the Contis are finished (which I am estimating will happen around 20,000 miles for the fronts).
Other good points: GREAT seats, decent cabin layout with handy flip-open compartment on the dash (although taller drivers might be annoyed with their right leg rubbing against the center console), high-quality leather covered steering wheel with nice white lacing, red gauges (although this is pretty subjective), decent 180W stock stereo (400W Rockford-Fosgate upgrade available)
Bad points: rear seats do not fold down unless you get the upgraded sound system (don't know what they were smoking there), rear spoiler is somewhat cheap and flimsy (rattles when you close the trunk)
Overall, for the price this car has no competition, and there are several more expensive sport compacts that this car can hang with.