For my no 1, I am going to rob @emjay82's No 2 - the induction noise. I think that eventually people will realise that the noise inside an IS-F will always be better than the noise outside. IMHO, any after market exhaust for an IS-F, GS-F or RC-F will spoil some of the pleasure presented via the induction noise (and add annoying boom).
2. Build quality - felt like a rock
3. Downshifting from third to second whilst braking hard for a corner. Loved doing that!
Of course, there were things I hated about the IS-F / RC-F, and here are three.
1. Gutless engine i.e. low down torque.
2. Wolf in sheep's clothing. Of course this is a major plus point (sometimes), but on ocassions, I really wanted people to notice that F cars are blimin mega. The RC-F sort of cured this.
3. 8 speed gearbox. Linked to number 1. Caught in the wrong gear, the box takes for ages to pick a cog. I'd end up driving it in manual most of the time, but you still had 8 ratios to ***** about with. Got to be on it when overtaking!