well it depends on what phone you had before, Previously I was using a N96/n95 so this phone was a little new to me but I was I used to having most of these features, so I can appreciate how well the n900 utilises its features.

1) for a phone like this the battery is pretty good, I haven't really had any problems
2) you can't use older software, but the amount of software available is pretty good, I found most software that I wanted and some that where just really interesting, but I'm still waiting for a media player with a equaliser
3) its the hardware wrong type of touch screen
4) It is big but it would fit in any pocket, personally I would never walk around with a phone on my belt.
5)There is a way of seeing you tasks, but you will need to learn a bit about linux/xterm
6)so far there are only a few emulators, but think about this you can install the android software on the phone so I guess theres lots of potential.
7)I tried out skype once and it seemed fine.
8) In my opinion the screen is perfectly sized good for quickly viewing sites maybe a little small if your trying to read from a distance but zooming is very easy
9) yes there are great games, the graphics are the best I have seen on a phone and all of them are free (check out bounce)

overall its a great device not the best phone.