So I bought Abathur because I thought he's a quite interesting character - very different from all the others out there. And indeed it is really fun for me to play him, even though there are some difficulties, one of which is to find a good role. My first of three builds was the "pusher" build. All-In on Locusts.
Pusher
1 - Survival Instincts (More health and duration for Locusts)
4 - Balistospores (More range and damage for mines)
7 - MULE
10 - Ultimate Evolution
13 - Assault straint (Cleave damage for Locusts and AoE on Death)
16 - Locusts brood (Spawn a group of Locusts with cooldown)
20 - Locust Nest (Place a nest that automatically spawns Locusts)
I thought that Ultimate Evolution is a nice heroic ability, since my Symbiote is rather weak, so I can use the time more useful controlling a copy. Aussault straint seems to be really nice for pushing due to so much AoE.
The problem with this build was, that its pushing strength comes rather late. Only the two lasts talents really justify the talents from before with great synergies. Usually by then games are more decided by team fights than pushing lanes. A very big problem was, that I had to be somewhere on the field to make use of the locusts. As the game goes on, the opponent bases are further away and my Locusts wouldn't even reach them. So I was hiding in bushes et cetera and changing my location quite often. Still I was found quite often too. Some Zeratuls even went so far to actively look out for me.
Healer
My second build was the healer. It was an impromptu, that I mad up because there was no healer in my team. It was astonishing how much heal you can do with Abathur. :D I could easily keep up with healers like Uther, but not quite Li li.
1 - Regenerative Microbes (Carapace heals over team)
4 - Sustained Carapace (More duration for Carapace)
7 - Network Carapace (Shield nearby mercs and minions, too)
10 - Evolve Monstrosity (Transform a minion into - well - a bigger minion :D)
13 - Soma Transference (Spike Burst heals)
16 - Still unsure on this one
20 - Hivemind (Two hosts for Symbiote)
Now this build solved the problem, that I could hide in the home base now in the later stages of the game. I could have the usual benefits (rocking team fights) of being a healer with their usual downsides (relying very heavily on your team mates). One big plus of Healer-Abathur is his invincibility. Normal healers can get targeted quite easily. Abathur stays in the fight from start to finnish and gets never oom, too. :D
The reason for Evolve Monstrosity over Ultimate Evolution is, that I want to spend as much time as possible spreading Carapaces to allies. It feels like Ultimate Evolution and Symbiote almost mutually exclude one another because you can only do one of them at a time. Same goes for the next build.
Assassin
My latest and favorite build. Not because the Healer build was bad, but because Li li is my highest level hero and I enjoyed playing her more. So I needed a new role for Abathur and here it is: The damage dealer in 1on1s and team fights.
1 - Pressurized Glants (More damage + radius and less cooldown for Spike Burst)
4 - Adrenal Overload (Attack speed for host)
7 - Needlespine (More damage + radius for Stab)
10 - Evolve Monstrosity
13 - Spatial Efficiency (Extra charge for stab)
16 - Envenomed Spikes (Spike Burst slows movement)
20 - Hivemind
It's quite amazing what big of an impact you can have on the game with this build. A hero is on trouble? No worries: Just jump to him and help him out. A lane is not getting soaked? You are there in an instant and even doing good AoE damage with Spike Burst. Especially after level 20, team fights are insane. You can do so much damage, as long as your two hosts stay close together. This build also has great synergies with melee heroes, especially assassins. The slow really helps them out and the extra bit of healing can make a difference in 1on1s or when running away. One downside of this build is, that you can help almost everywhere and you have to decide where you are needed the most. But you also don't want to waste time out of the Smybiote, so you do one thing, look out for the others etc. at the same time. It's actually quite a bit of multitasking to do, when you combine it with laying mines and changing locations. So this play style is not as relaxed as others.
Abathur in general
Now let me write a few words about my experience with Abathur in general. First of all, I like his diversity. He can do almost anything, depending on how what build you use (initiator and tank will be difficult though :D). I like his "abstractness" of being nowhere and everywhere at once. But there are also a lot of down sides:
He is not understood by the others. I believe most people don't really get what Abathur is doing, during the game. Often times, people complain about having to fight 4 v 5 all the time. A great deal of people also think, that Abathur is a pure pusher who is pushing his one lane all game long and does little else. In short: The great value you add to the team is not seen, not even in games likes this (Assassin build)
If you are one of those guys who rage over "noob allies", Abathur is not for you, because you are maximal reliant on you allies to act properly. If everyone is running around like a bunch of chickens, there is little you can do. With some other heroes you can at least fill in your role and push a lane or something.
All in all, Abathur is a really unique and fun hero to play. Even though he is not very much appreciated by your team mates, you can add a lot of value to your team, as long as there is some team play. Abathur is definitely not a hero, who can turn a game around single-handedly.
Maps
Personally, I prefer maps with big team fights for Assassin-Abathur, when there are many small fights going on, its hard to make the right call where to help. Switching fights costs valuable cool down time. For Pusher-Abathur I didn't like big maps, especially with little hiding places. My ranking is as follows (Assassin-Abathur):
Sky Temple > Cursed Hollow > Haunted Mines = Garden of Terror > Blackheart's Bay >> Dragon Shire
Conclusion
Thanks for reading. I hope you took something out of it. Maybe you'd like to post your experiences with Abathur? (As a player or as a team mate)