I belive the Maxima and IS300 are very much comparable - indeed, both were among the "finalists" of my recent car-purchase decision. I had a '98 Accord Coupe V6, which was an excellent car in all respects save that it was not particularly fun to drive. All of my previous vehicles had been stick-shifts, and I felt a return to "rowing my own" would significantly improve the fin to drive quotient. I also wanted a V6. The three finalists were the Maxima, IS, and CLS. Yes, I know that the latter two don't have stick-shifts, but the engine on the CL-S is a compelling argument all by itself.
But returning to the Maxima / IS300 comparison. Let me say at the outset that I was really very fond of the IS - there's a lot to like about this automobile - but I chose the Maxima. Here are a few of the rambling reasosn why.
1) 5 speed stick. No "manumatic" truly replicates the 3-pedal experience. The IS 300 autoshifter is excellent, but it's still an automatic.
2) Sensation of speed. The IS 300 just doesn't feel fast. In fact, I didn't come across any publication quoting a measured 0 to 60 of less than 7.5 seconds. A recent Canadian publication had it at 8.0 seconds, and that's how it felt to me. I think the two-fold culprit here is the auto box and vehicle weight. I was surprised at the fact that the published curb weight of the IS is greater than the larger Maxima. The IS needs to go on a diet, plain and simple. And it's not absolute numbers that concern me so much as the sensation of speed - windinng out second gear in the Maxima, up-shifting to third, and feeling a whole new rush of acceleration is an experience I just didn;t get in the IS.
3) Exterior styling. IS 300 wins by a long shot. In my opinion, it's the best-looking compact sedan available at any price. The Maxima design has, shall we say, less universal appeal. But I like it, and I spend more time inside than outside the vehicle.
4) Interior design. I found the Maxima the clear victor here. Clean, legible and elegant dash design. Quality materials. The dash on the IS is something that I would be resigned to putting up with, simply because there is so much else to like about the car. And the rock-hard plastics that are not evident in any other Lexus didn't even measure up to my Accord. Also a serious lack of interior stowage space. Lovely leather seats with contrasting piping, though.
5) Handling / Braking. The IS 300 was the winner, but not by as significant a margine as I would have thought. I'm a big fan of RWD, but I also live in Canada where, as you might have heard, it snows. RWD is a whole different kind of fun in winter - and not a good kind.
Overall, I found the Maxima to be more fun to drive, which was my primary purchase criterion. The fact that it was SEVERAL thousands of dollars less was simply a bonus. It's not that I couldn't afford the IS, but having an extra large load of cash available to play with was a nice treat.
My next car will probably be the IS - when it is available with a 5 speed (6 speed ?) tranny.
And by the way - this is a great forum - I learned a lot here when I was in pre-purchase mode and will certainly keep looking for any updates.
Have fun
Jaeger