Wind the clock back a few years to a time when DSLRs were beyond the reach of many amateurs, and there were various other options in the digital world. Canon had the G series with RAW capture, and also the Powershot S series - the same sensor in a smaller, pocketable package. These made excellent compacts for DSLR users, too, and I bought an S70 which I used for quite a few years, which proved itself an excellent bit of kit. Then Canon lost the plot - 2005's S80 replacement for the S70 lost RAW capability, and just when this type of camera was coming into its own, Canon dropped the series.
Until now. The S90 is very much in the spirit of the S70 - it shares a sensor with the G11, as the S70 did with the G6, and has RAW support. And it's much more pocketable than the G series. Now call me radical, but I like my compact cameras to be, well, compact. To fit into a pocket and go anywhere with me. The G series just can't do that. The S70 pushed it a bit - it was long and chunky, not helped by the use of Compact Flash cards and the same battery as the lower-level EOS cameras. But the S90 ticks that box perfectly; it's the same height as the S70, but a lot thinner and less deep, and despite the lens ring, fits so much better into just about any pocket. And it has a lens with a very similar equivalent focal length range of 28-105, as against the 28-100 of the older camera.
In terms of design, the S series has changed; the S70 had a sliding protective cover in front of the lens which looked good, but could get fouled by the strap, preventing the cover from tripping the microswitch that turns the camera on. Rather infuriating. The S90 uses an on/off switch, and the built-in lenscap type lens cover. Some have said the power button is in an odd position - perhaps it is, but it works for me.
In terms of design, then, things start off differently, and so it continues. The S70 has a 1.8" LCD display, and 10 buttons, a 4-way rocker and a zoom rocker on the back of the camera, the mode dial and shutter button on the top plate, and the connectivity sockets on the side under a rubber cover. It also has a vestigial optical viewfinder that displays 80% of the image area. The S90 dispenses with this rather useless appendage in favour of a 3" display with a lot more dots. It also reduces the number of buttons on the back to 5, retaining a 4-way rocker but adding a rotating wheel around it. In addition to the mode dial, zoom nudger and shutter release, there are two buttons on top, the power button already mentioned, and one to control the lens ring. And then there's the lens ring. Now there's a bit of brilliant design - the lens ring is wonderful. You can use it to set the aperture, which feels so natural to those of us brought up in the old mechanical days. It can also control the ISO, manual focus, white balance (to dial in more red or blue), zoom or exposure compensation, and you can use it for different things in different modes. Add in the customisable Shortcut key on the back, and the My Menu options, and you can set this camera up very much how you want it.

So - pick it up. If you use it at arm's length, your finger doesn't find the shutter button, and your left hand falls on top of the pop-up flash. Now of all the pop-up flashes I've ever seen, this one pops up with the most confidence - it's a beautifully-designed mechanism.
However, if you hold it as it's clearly designed to be held, much closer to your body with your elbows tucked in, not only will you get a much more steady grip, but the layout of the controls becomes perfect. The little bulge for the mode dial becomes a thumb rest; the index finger of your right hand falls on the shutter button; and your left hand supports the bottom of the camera and the lens ring, ready to change whatever function you've set. There's a lot of thought gone in to this design.
In use, it feels very much like a small DSLR, at least a Canon one - the two control wheels mean you don't need to look at what button you're pressing or delve into the menus too often - but you can control the camera like a more traditional digital compact if you want to. But it also feels like a much more traditional camera than almost any other digital camera I've used - the tactility of the lens ring and pop-up flash make it feel far more mechanical, and far more German than any other digital I've used - it has the feel of a Rollei, and from me, that's about the highest praise you can get.
The screen is excellent, and copes well in direct sunlight. Mine displays a live histogram and a grid - which is in thirds. The rear wheel feels a bit odd at first - no click stops - but that again reminds me of Rollei, as the shutter speed dial on the SL35E didn't have any either. I'm surprised I don't move it accidentally, but I don't - and it actually feels very precise in action.

Couple of other things I've not mentioned yet - the lens is f2, at least at the wideangle end, it has Image Stabilisation, and ISO values to 3200. Now the old S70 went up to just ISO 400, and was pretty noisy at that level - the S90 is at least two stops better, with 400 perfectly usable and even 3200 usable.

Which brings us to image quality. The S70 produced really rather good images at the bottom of its ISO range from its 7.2 MP, better than many more recent compacts with overstuffed sensors. The S90 certainly seems to produce very good results up to ISO 400, and usable ones beyond - given my expectations of a compact, anyway. There is a "but", and that's the level of distortion the lens produces. Opening a RAW image with ACR, there's a lot of barrel distortion at 28mm equivalent - but in Canon's DPP, straight lines return to normal as if by magic.

So, all in all I think it's more than a fine return to form for Canon with the S series. This little camera is a masterpiece way in advance of the earlier model in every way I can think of - it looks better, feels better, performs better, fits into a pocket better and above all, takes better pictures. I love it, in case you haven't guessed.