OK, I've owned a G1 since day one. Bought it (loyal T-Mobile Customer) and I've enjoyed it totally. Nice part is, I've got an iPhone in the house thanks to my wife so I can compare. Both her 3G and my G1 are around the same age.
Reliability, Her iPhone has had to go back to the Apple store twice due to problems one got it replaced (internal error, infant mortality) and the second resulted in a full factory reset cause by an Apple supplied update.
In the reliability dept I've had the edge. Nothing has gone sideways. I've reloaded the OS yes, but by choice (I've rooted mine, I like to tinker) otherwise no complaints due to early death.
Battery life: Ok hands down. You have to buy a bigger battery, second battery, 2nd charger and a car charger. The G1 batter starts out under spec'd and goes to hell in a hand basket from there. I've upgraded to a 2400mah battery and unless I'm doing multiple hour long calls in one day, it's easy to go 1.5 to 2 days on a single charge.
Apps: In short the apps store rocks. I can read and edit .docs and spreadsheets. View Presentations and PDF's Keep up with E-mail and more. On top of that there is an ever increasing number of other apps and games. Not to forget the #1 game, Pacman.
For the Sys Admin side of my life the #1 app is ConnectBot. This is an SSH client with the ability to use ssh keys. A must have for sure. Nagios and Monit also have clients, and the browser does work well with MRTG and Munin. There are also tools for reseting/restarting Wake on LAN enabled boxes, a Terminal emulator, and finally some tools for checking if servers are alive.
In short when it comes to the app zone, no the G1 does not yet have the shear number that the iPhone does, but by golly it has all of the essentials and they work well. My phone has a good mix of free and pay apps and in general even without the infamous iPhone standards board the apps are really good. Heck the G1 even has flatulent apps.
G1 as phone: Here is where the G1 starts to fall down. The biggest problem stemming around the shear number of times you need to keep pressing buttons to keep the screen from dimming out during a call. Especially frustrating if you are using an IVR system. Instead of pushing 3 it's menu/menu/wait/3 (as they go into the second iteration of the the numbers.) over and over. Most of this is IMHO due to the fact that HTC knew they had skimped dramatically on battery and they are trying to the point of annoyance to keep from using it.
Additional problems when using it as a phone come in the way it interfaces with a BT headphone. Most phones allowed me to press once on the headphone to answer a call or to connect to voice dial. Unfortunately the G1 doesn't seem to accept either of these commands. This means I have to pickup the phone dial or to answer. A big hassle if you live in CA like I do. (Cops are looking for phone's in hand big time)
Data input: This is where the G1 shines. The thumb keyboard is well layed out, tactile feedback is great, most important is how they overlayed the keys from a 101 key keyboard onto a much smaller form factor without causing undue hassle in reaching the popular keys. Nokia's N series could take a real hint from the Android keyboard (on screen and slide out). You can even send long e-mails from the phone as long as you don't set it down. Seems that if the phone detects a pause while composing in the G-Mail app, it auto sends the mail (grrrr). Otherwise. I love this aspect.
Network: I live in the SF Bay area. For me everywhere I go except inside a Fry's I've got 3G. Speed is great. I'm able to watch a YouTube video with only the rarest of re-buffers happening. Syncs to mail etc happen quickly. When I went to Yosemite last year, yes out in the middle of no where in Northern Indiana I did lose the 3g but kept the net, slow but there.
So all in all would I buy a G1 again. Yes I would. I really love what it offers me. I love the FOSS features and the community. It really allows me to fit the phone to me. Ups are data input, feature set and form factor. Downs are phone related UI, and battery life. Overall I'd give the G1 a solid 7. On the other hand I would not want an HTC phone again.