Is it just wattage? I'm getting crosseyed from reading the specs over and over.

249, the difference in watts is of little significance; from 90 to 120 watts is only a difference of 1.25dB in volume on peaks(e.g. 110 or 111.25dB). Other minor differences may be attractive to some, but probably the major differences between the two are the automatic calibration and equalization on the 3805 and DPLIIx, which can extract the ambience in two and five channel material out to as many as seven speakers.

There is a 2805 model as well.

3805
1) Upconverts video
2) Has Autoequalizer (although there are mixed reports of its accuracy)
3) Has Pure Direct Stereo (better 2 channel than 2803)

Other than the differences mentioned here and above, the 2803 is a pretty nice choice and can be had for a good price these days. Frankly, unless you intend to take full advantage of all of the features of the 3805, the 2803 is a great value.