I started Retribution a year or so ago as equal parts painting project and legit second faction. Retribution has a similar approach to Khador in how it handles the game: excellent infantry backed up by warjacks, with 'casters offering the support.
The difference is mainly in the portions. Khador has great infantry, so-so warjacks, and excellent warcasters that in many cases can legit close games on their own. Khador tends to operate with a combined arms approach that leans towards melee, and their ranged damage is unique in that it has loads of blast damage and sprays.
Retribution has fantastic infantry, so-so warjacks, and good warcasters that offer excellent support, but aren't usually a big force on the table themselves. Retribution tends to operate with a combined arms approach that leans towards ranged attacks, and their ranged attacks are typically direct attacks with a variety of bonus effects and/or things they ignore.
The armies are similar, but flipped. Retribution also has the virtue of being a newer faction, so it feels like they have a lower percentage of "chaff" models than Khador does, though their warcaster stable is probably honestly not as well balanced or versatile as Khador's is.
I knew all of that going in, and I was ultimately excited to play Retribution. It isn't a huge gear change, but it is a different enough approach to the game to be a novel experience, and the suite of abilities that Retribution brings to the table makes them a very interesting faction to play.
I also made myself a promise: barring exceptional circumstances, I would not play any Retribution models that are not painted. I made this mistake once before with my Legion army; I kept collecting and collecting, playing without painting. When it finally came down to sit down and paint some of it, I looked at my collection and realized that a) I didn't really like the look of the models enough to paint them, and b) I owned a ton of stuff I was never going to use again, and therefore didn't want to paint. That (combined other factors) led me to sell off my Legion and consolidate my efforts into Khador, with an eye on picking up another faction or two again down the road.
This time, I'm doing it right. No more buying a ton of stuff, then playing catch up on the painting table for years. No more collecting things just to say I have them; if I think it sucks and I'm never going to use it, I'm not buying it.
Ironic, then, that I chose to start off this project by buying probably the Retribution warcaster I like the absolute least. I opted to start my Retribution army when the plastic battlebox was released, which includes Kaelyssa, a Griffon, a Manticore, and a Chimera. I felt like I could find homes for the other three warjacks (at the time the Griffon and Manticore were generally well regarded, and the Chimera has grown in popularity,) so I figured at worst I'd end up with a warcaster that I didn't like that much.
I built a list based on what I thought would work alright with Kaelyssa, while also giving me some good starting points for the rest of the army:
Kaelyssa, Night's Whisper (*7pts)
* Chimera (6pts)
* Banshee (10pts)
* Manticore (8pts)
* Sylys Wyshnalyrr, the Seeker (2pts)
Dawnguard Sentinels (Leader and 9 Grunts) (9pts)
* Dawnguard Sentinel Officer & Standard (2pts)
Lady Aiyana & Master Holt (4pts)
Mage Hunter Strikeforce (Leader and 9 Grunts) (8pts)
* Mage Hunter Commander (2pts)
Mage Hunter Assassin (2pts)
Mage Hunter Assassin (2pts)
Part of this is cheating: I already had a painted Sylys and Aiyana & Holt, but I wanted them in the list for general utility. I also painted up the Griffon that came in the battlebox to have for later, since it's a very useful 4 point light (even if it didn't make the cut this time.)
The good news is: the plan worked! I managed to get everything painted before playing the list, and much to my surprise the list even worked decently well in the two games I played with it. I now had at least one fully painted Retribution list, and a lot of building blocks in place to let me pretty easily paint up new 50 pointers.
That leads me to where I am now: I have zero clue where I want to go with the faction next.
I picked up a unit of Invictors + UA since they're excellent infantry that show up often, and that will be the next "big" thing I paint for the faction. Aside from that though, I don't really know what my next steps are going to be.
The Retribution warcaster that interests me the most is Vyros2, but of course the reason he interests me the most is his bizarro play style (almost universally: a glut of light warjacks.) That means that very little of what I've done so far will carry over into his list, so right off the bat I'll need to paint a lot more than I probably want to in order to get a second, more exciting list on the table. And then there's the complication that I don't really know how I want to build a list for him - the "classic Pagiani" style of list has 9 lights, which I don't think I want to do, but even if I pare that down I'll probably end up with something like 4 Griffons (so 3 new ones.)
Rahn and Ossyan are also very interesting, but they kind of call for different enough infantry bases to seem like they'll be more labor intensive. Issyria is a very clean fit for what I have now, but I really don't want to run her without a Hyperion and I'm not sure that I want to be buying one of those this early into the faction.
Garryth is a warcaster I find amusing, but flawed, so I don't want to get sucked into building lists for him (at least not yet.) That leaves Ravyn and Vyros1 as warcasters that make the most sense as a "next step." Ravyn is another one I'd like to have a Hyperion for, but it wouldn't kill me to run her without one, and she'd do alright with the infantry I have now (MHSF + UA are broke with her, Sentinels less so.) Vyros1 does a better job of tending to the Dawnguard (kinda sorta) and makes use of oddball heavies a little more effectively, but he himself is pretty janky and I know I'll want to replace part of his battlegroup with Imperatus when he comes out. The good news is, Imperatus in general makes Vyros1 much more interesting, so I don't feel nearly as bad going with that option as a "next step" choice as I used to.
I think no matter which one I choose, my next Retribution 'caster will be one of those two. Vyros1 may end up being the winning candidate since I can use that as an excuse to paint up some models that may splash out into other lists - particularly warjacks, which paint up pretty quickly in the paint scheme I'm using - and I feel like I'll have the infantry in his list already covered (whereas I'd probably want a different unit in Ravyn's list, either instead of Sentinels or as a 3rd.)
Then there's the matter of affording the next chunk of the army, but thankfully I'm working slowly enough that I can pace my spending into DiscountGamesInc.com friendly $50 chunks. The next step is going to be painting those Invictors, and figuring out what the next chunk will be!