I managed to get some playtime with the oozemorph and I've got to say that it really was a blast. We were playing at level 3 so I took 2 levels of oozemorph and one of unbreakable fighter while focusing on Dex and Con, using weapon finesse to make sure I'd hit and saving my humanoid shape with light armor for the dungeon we entered. Having 21 AC combined with DR4/Slashing really was amazing, I really felt like a blob which could just get punctured and slashed without any problem. In blob form, not being able to be flanked or crit actually came up and was a great help too, the much lower AC of it was a bit of a bummer.
Now for some of the downsides, being a blob of ooze is obviously difficult in roleplaying situations, for a one-shot it was fine, I could do some silly things, (and almost got blamed for the disappearance of the local pets) but I can imagine that in a longer campaign that starts at level 1, being an ooze could be quite troublesome especially the no talking part. We discussed that having some sort of second humanoid shape that falls apart under stress (i.e. combat, lifting stuff or somebody poking you with a needle to make you pop) would really help out, without removing the penalty.
Another thing is that you need to not have a GM that feels like it's him vs the party. As the DR can get pretty high, especially if you go bulky as I did going for things like stalwart at later levels, and some GM's might start having everything carry slashing weapons.
Finally not being able to deal with types of DR other than the basic damage types is a big bummer, we encountered an enemy with DR5/magic and that felt bad, I can only imagine DR10/magic. I carried a light crossbow myself to deal with flying enemies, might be useful to do that for different damage types too.
All with all, I really liked playing it and I would definitely play it again, albeit at a higher level where more of the ability's are available. I do sincerely hope we'll get some sort of errata or update from paizo though, as it feels a bit bare bones with all the empty levels.