I owned the C-750UZ, which still used four AA cells. My understanding is that the C-770 focussed faster and did not show broad over-sharpening like the C-750 did.
Like you, I find that my C-750 pictures are priceless -
Although I kept my C-750UZ in use until 2007, I would hesitate to do a review about it NOW. You can no longer buy either the C-750 or the C-770. My SP-570UZ, although also now a historic relic - I bought mine in 2008, outclasses it in everything except size. The SP-570UZ is BIG.
Regarding battery life, Li-ions don't last forever. I saw somewhere an Olympus statement saying they are good for 300 charge/discharge cycles only. You might try and find new replacements for your C-770UZ batteries. Some of the third-party suppliers might still flog them.
Thinking of my past user reviews, they tend to be positive, taking into account what is available at that time. I also work around any shortcomings. But with some of my previous cameras, I get nostalgic about the pictures I took with them, not necessarily about the cameras themselves.