Both flights were Combi 747s.

The moment you book your flight, call in to get seat assignments. I was not aware of this, and by the time I called in 1 week prior to departure – the only seats left were middle seats. Get there early if you were not able to secure a seat of your liking. There are 11 rows, 4 of which are bulkhead and/or exit row seats that are controlled by the gate. At SFO, this means being in line by 10:15AM, regardless of flight time. We were there at 10:15 for a 2:50 flight. Yes, horrible, but consider it the cost of not getting trapped in a middle seat for 12 hours.
Luckily, our party of 4 was able to get the 4 seats in a bulk head row. This probably made the flight much bearable for me – I’m 6’3”. It’s also nice that the two people sitting in the middle seats could get out at anytime without disturbing the two on the aisle seats.
Check in itself was uneventful. I did notice that they were holding people to the weight limit. There was much repacking done at the check in counter.
We were in the 50s, and this being a combi jet, we were in the first group to board. CA boards from back to front. I’m Chinese, so I’m qualifying myself to say the following – When you’re boarding a Chinese carrier (includes HK, Taiwan, China), when they call first class to board, this is your cue to move as close to the gate as possible. About 30% of the economy passengers will bullrush the gate the moment the announcement for economy is made – regardless of their seat assignments. I don’t know if they’re not listening to the seat call outs, they just want to ignore the system and get on even if their seat block hasn’t been called or if they are just used to packing up lines. Luckily CA actually turned away passengers who's rows weren’t called.
I suggest you do this if you want prime carry on space. If you don’t care, or need space, then let the crowd pass.
The seats themselves were normal 747 seats, no different from AA or UA economy.
Food was ok. The first meal, served 1.5 hours into the flight was eggplant-pork or chicken-longbeans with rice. The sides were, salad with 1000 island dressing, dinner roll and fruit. I felt like this meal was comparable to meals on EVA and Cathay that I had recently – except that it was lacking a true dessert (cookie, brownie etc). Second meal, served 8 hours into the flight, mains were shrimp-veggie stirfry with rice or beef and noodles. I had the beef and noodles which were drowning in oil, I didn’t finish it. Sides were some kind of coleslaw type thing, dinner roll, and a pineapple ‘shortbread’ (fenglisu). I didn’t touch the coleslaw. The second meal could have been a little better. It might have been different had I been more hungry (I ate my own mini meal before they served).
The one aspect of food that was noticeably different from EVA and Cathay were the snacks. CA basically had a basket of crackers (open a box and dumped in a pile) sitting next to the self serve beverages. Cathay had instant noodles, packs of crackers, chocopie cakes etc. EVA has packets of nuts, crackers, and sweat biscuits. On CA, nothing was served with the beverages, and no snacks were handed out.
Cabin was warm! My travel companions didn’t feel all that bad, but I thought it was sweltering.
Service was functional. They met requirements, but I didn’t see any real hospitality – what I’ve come to expect on international asian carriers. In fact, a number of our FAs were practically stone face expressionless.

Flight returning was probably on the same aircraft.
Sat in a regular center section with my family. I actually slept for 7 of the 12 hours in a middle seat. I think the seat pitch is indeed 1" more than normal. Felt not bad to me.

Note, bring something to do on these flights. There is there are 2-3 movies shown on the big screens. However, the video quality is so horrible (likes, snow, skips) it's not worth watching. Food was meh. Slightly lower quality than the other Asian carries I've been on.

Also went on a couple of domestic flights. Seats were closer to the 31" pitch. It was tight! Was on a 737, A310 and A321. Same kind of food. No entertainment. Gets you from point A to point B. No problems with check in, seating, take off/ landing.

Besides the SFO - Beijing flight, all other flights were boarding free for alls. Line up if you want to get on early.

All in all, for budget traveling, or in my case - flights included with the tour; Air China got the job done and it wasn't horrible. There is no need to fear Air China.