12.3 Megapixel High Speed Live MOS sensor and TruePic V image processor. We don't know for certain but we'd expect this to be the same sensor as used in the Panasonic G1 and Olympus E-30 (the total pixel count of 13.1 million pixels rules out it being the newer multi-aspect sensor used in the new Panasonic GH1). The latest 'V' version of the TruePic sensor is claimed to improve processing speed and to allow the E-P1 to offer ISO 6400 (a first in an Olympus Four Thirds model).
Interestingly we've been told that the new sensor has a lighter anti-alias (low pass) filter than previous Four Thirds models (which Olympus confirmed have quite strong AA filters) with the new processor able to almost completely remove the resultant moiré at very high frequencies (i.e. high resolution without color fringing).
Micro Four Thirds mount. The E-P1 is the first Olympus model to feature the new Micro Four Thirds variant of the Four Thirds system. Micro Four Thirds does away with the mirror and allows for smaller, thinner cameras and lenses.
As there is no mirror and the camera works in live view mode full time, the E-P1, like the Panasonic G1 and GH1, features a newly-designed vertically traveling focal plane shutter that stays open when powered down (conventional shutters are closed when powered down). This makes MFT cameras rather unusual in exposing their sensors when the lens is removed.
Sensor-shift image stabilization system with a claimed 4 stop advantage. We believe this is the same unit used in the E-620. The Image Stabilizer isn't used for movies (which get 'Digital IS - electronic image shifting - which isn't the same thing, but does seem to work).
HD movies with stereo sound. The E-P1 can capture 720p HD movies (1280x720 / 30fps) in M-JPEG (.AVI) format. You get control over aperture if you want and can use the art filters in movie mode (though some will seriously reduce the frame rate).
HDMI connectivity. The E-P1 can be connected directly to an HDTV screen using the built-in mini HDMI port.
New 3.0" Screen. The EP-1 sports a new large Hyper Crystal screen. Surprisingly the resolution is only 230,000 dots (we had expected at least twice as many).
Art Filters. The EP-1 gets all Olympus's latest gizmos including Art Filters (the same 6 seen on the E-30/E-620). There's also a huge range of scene modes, aspect ratios, multi-exposures and a new 'e-Portrait' mode (designed to blur skin to remove wrinkles).
SD Card. In a camera this small there was never going to be room for the dual CompactFlash / xD slots used in E-series DLSRs. Thankfully Olympus resisted the temptation to make the E-P1 xD-only, instead opting for an SD/SDHC slot. If this signaled the beginning of the end for xD in 4/3 SLRs I don't think there'd be many tears shed for the increasingly redundant format.
Dual Control Dials. The EP-1 sports two command dials - one around the four-way controller and this unique vertically aligned thumb dial. The dials are highly customizable (usefully either can be assigned to AE compensation).
New Accessories. Built to be as small as possible, the E-P1 lacks both built-in flash and optical viewfinder. Flash-wise you can use any Olympus FL unit (including the new matching FL-14), and if you want an eye-level finder, there's the new VF-1 (which attaches to the hot-shoe and offers the same field of view as the new 17mm pancake lens).
New Lenses. At launch the E-P1 will be available in a kit with one of two new lenses. The first is a neat collapsible 14-42mm (28-84mm equiv.) zoom, the second a very slimline 17mm F2.8 (34mm equivalent) 'pancake'. More lenses are promised.
Lens adapters. Of course you're not restricted to the two new lenses. With the MMF-1 adapter you can use any Four Thirds lens too (and Olympus told us that the aim is for all FT lenses to autofocus on the new camera).
Interestingly Olympus is being a lot less precious about the use of non-4/3 lenses with the new system (the press release talks about 'adapters for lenses made by other manufacturers). For its own part Olympus is launching an OM adapter (the MF-2) so you can put all those lovely old Zuiko manual focus primes on the new body. You only get stop-down metering (but the metering does work and you can use Aperture Priority mode).
New Live Control Interface. As a live view only camera the E-P1 gets a new interface that gives you access to all the most commonly used settings without having to enter the menu system. It's very much like Panasonic's Quick Menu (amongst others).
One welcome touch is that you can now preview the various Art Filters without having to go back to a menu. You can now apply Art Filters to saved Raw files too. Both of these were issues we complained about in our review of the E-30, so kudos to Olympus for listening to its users.