I've just traded in my EOS-10 for an EOS-1N HS. The new camera is lovely - a bit heavier than the 10, but it feels fantastic. It's so solid, the controls are almost all just right. I love the extra shutter release and exposure lock buttons on the grip, for more comfortable ergonomics when shooting in portrait orientation, and the way the DOF preview button is just as accessible in this mode. The extra strap attachment is good, too. The less-often-used controls are hidden away under a flap, although I sort of wish the drive mode button wasn't as it makes it a faff to turn high-speed continuous wind on for taking bracketed exposures (and if you leave it on you end up with 2 of each picture, so quick is the drive...)
Everything feels sturdy, unlike the weak rotary-dial-with-lock-that-often-breaks on the consumer EOSs. The 100% viewfinder is great, and the viewfinder shutter is a much neater solution than putting old film can caps over the viewfinder. The "shots remaining" display that shows when there are fewer than 10 remaining exposures on a DX-coded film is very handy, as is the choice of loud-but-fast or quieter-but-slower film rewind speeds. The metering system is excellent and simple - there are only 3 modes (a good evaluative metering system, centre-weighted average metering and spot metering that can optionally be linked to the selected focus point) but these are the only ones I would want anyway. The EOS-10 had highlight and shadow metering modes, accessible by writing custom barcodes for the otherwise-useless EOS barcode reader, but I don't know of anyone who ever used them - I certainly never did.
However, I really wish that, when using the back-panel dial to select the focus point, it would let you select auto focus point selection using this dial instead of having to switch back to using the exposure compensation button plus the main dial for this. I find it the best of the custom-function-selectable variations on focus point selection but it still feels really clumsy - the only weak point in an otherwise impeccable set of ergonomics.
Next, it's so fast! First, the speed of the autofocus is a great improvement over that of the 10, and second, the continuous-shoot speed: 6fps! Yes, that means you could get through a whole 36exp film in 6 seconds, but more importantly it means you can take a set of 3 exposure-bracketed shots in half a second.
Oh yes, and if you're into shooting IR film then this EOS is fine; it doesn't suffer from the problems many EOSs do with IR film counter diodes fogging the edge of the film as it uses a sprocket counter (for those who care: the EOS-10, EOS-1 and EOS-1V are also fine). It also has a solid backplate so the reflected IR won't look weird. (See photonotes.org for a fuller explanation of this.)
The battery life seems fine too: it does use 8 (!) AAs, but they last for about 65 36exp films and NiMH rechargeables will bring the cost down anyway.
In summary: the EOS-1N is a big step up from the EOS-10 in terms of both quality and performance. It is well-designed, feels extremely sturdy and has already produced excellent results. The interface is in most respects just right - everything you want is there, where you want it, and the cruft no-one ever uses has not been included just for the sake of it. It doesn't have the eye-controlled focus, number of autofoci or extreme weatherproofing of the latest EOS bodies (the 3 and the 1V), but neither does it have the price tag. Until 2000 it was Canon's flagship SLR and for less than 600GBP it is an extremely good value buy; I'm very pleased with it.
Note: I'm currently using it with the EF 50mm f1.4 USM lens and a x2 teleconverter, which are also awesome pieces of kit; I traded in my 35-135mm zoom with the EOS-10 body, and aim to replace it with a 28mm prime and some kind of good telephoto prime, either a 200mm or a 300mm. I'm also using a Jessops flash, which totally sucks and doesn't even take rechargeable batteries because the battery chamber is too tight a fit, but I don't do that much flash work anyway..