Shadowrun Returns

Basically you can stop at 6 in almost any stat, and you'll be fine. The only exceptions seem to be chi casters and riggers, they actually get upgrades all the way.

Quickness - The accuracy boost is noticeable for sure, but 6+2 (2x leg cyberware) is plenty. Not being able to actually use Double Tap at Rifle 6 was very disappointing, and I ended up raising Shotgun to 6 as well instead of wasting more on Quick/Rifle. Kneecapper on overwatch and the burst attack from the auto-shotgun were very handy. Dodge I kept capped out to the same level as my quickness (+2 from upgraded leg implants) and it seemed to help a lot. Other runners took a fair bit a damage in missions, while my decker was never even close to being in danger even before I raised Body up.

Strength - I assume it's the same deal with the bugs as quickness, but that's for the next character.

Int/Decking/ESP - 5 was plenty except for the one 6 check which is only 1500 nuyen anyway. Decking isn't as bad as a lot of people make it out to be, but I never used the to-hit buff at all and I let the elf dude do the decking in the serum mission. ESP I found to be completely useless and put zero points into it. Never used medkits at all either.

Charisma - 4 is plenty for all conversation checks, and the only etiquettes that have any real benefit are Shadowrunner and Academic. Corporate and Security showed up maybe 2 or 3 times each, but they don't actually do anything special. Shamans don't even seem to get a whole lot of benefit past 6 either, just Hellstorm Barrier.

Body - I took this to 9 (elf max) and had 89 hp at the end of the game, despite having two of the upgraded leg implants. Still, there was nothing else worth spending points on.

Willpower - 5 seems like a good amount even for non-casters. Spells missed me a lot as long as they weren't AOE. Mages get all their spell slots/unlocks at 6, and only chi caster spells have the really high reqs.

Total karma in the campaign is 229 if you're curious, unless I missed something. Almost too much really, given the lack of any real need to raise individual things past 6. For people making their own campaigns, I would probably suggest to keep it down around 190-200.

The basilisk creation facility from the alpha game play footage no longer allows you to run to the terminal on the wall and gas the basilisks so you don't have to deal with all of them, and you didn't actually have to sluethe out the locaton and get in any pre fights either. You just got the quest handed to you in the Seamstress' Union and get teleported to the facility.

In the first mission where you're rescuing Coyote, there's the hidden stairway up to the top. In addition to being able to open it with a CHA 4 or STR 4 check, there's a CHA 3 check only visible if you know the stairs are there. Also, a rigger can use their drone to open the door, and a shaman can summon a fire elemental on the stove in the apartment that causes the occupant to open the door.

I noticed a bug involving the vents and other areas the Drones can get into... some of these vents will reduce your drones available AP by 1 permanently. At least this happened during the last mission. Drone should have had 3 ap with the bonus, but was stuck on 2 ap all the way to the final boss fight.

Stacking the decker marked target skill, the mage aiming buff and full auto is a good way to kill anything in 1 round.

Double tap seems to increase the crit chance of the double fire mode on rifles.

Some silly exploits can be had with drones in certain areas being able to pop out of a vent, shoot and pop back in until everything is dead. Really tedious and boring to do however.

I stacked armor at the end using the 10 armor suit and dermal plating. I only had 5 invested in body and never really felt like I was in danger. I also stayed back and used cover, letting the drone scout out ahead. Armor does reduce damage taken by a good amount. I think it might effect the chance that enemies do a weak strike against you as well... not entirely certain on that though.

I think most missions can be soloed except for where the game forces you to have a partner, the decking phase of the aegis mission where the security groups are attacking from the two elevators and possibly the final boss fight.

Agree with Vorph about CHA, just get the 2 he recommends and leave it.
The final level was a humongous pain in the ass. Having the bugs go ghost and then stripping 2AP from your Aegis wielders was just tedious. Whatever asshole put a -AP attack on the ghosts needs slapping.
I ran with me (decker) using pistol, the 16 dam one you get at the end seemed fine.
The dwarf utility mage is pretty damn useful, although keeping him alive was a pain. Seeing a heal land for 1 on a char with next to no HP makes you cry.
I ran with the +1 INT decker armor. It was useless.
Harlequin seemed under powered to me. Maybe I just enjoyed that campaign book too much