I completed Alkaline a couple of days ago (including the 4 secret maps). Almost all of them were atleast pretty good (except a couple of secret maps, which I assume are repurposed old maps and felt a bit basic, but still okay) and half of them were atleast great. With that said, these were my 5 favorites:

5. Foundation for Corruption by Mista Heita
Really cool dystopian almost-cyberpunk setting is an automatic huge plus for me as I am fan of such aesthetic and would like to see more of it. But the map itself is also really good with tight gameplay and spicy encounters. Only nitpick would be that once I reached the rooftop, I decided to jump on another nearby building. Well I landed on their rooftop, thinking there might be a secret, but ended up dying :p

4. Tallus Terminus by zigi
What a beast of a map. Took me around 1.5 hours on first playthrough. It being the first Alkaline map I played put a really strong impression on me, especially when going down the first lift and saw the station from the lift windows. Good mix of indoor and outdoor action. Has a very big difficulty spike when you pick up the invisibility and have to fight those railgun robots in a small room. But otherwise, smooth sailing.

3. Geothermal Outpost by Greenwood.
Loved the verticality and the general Doomcute (or Quakecute in this case :p) of this map. The infinitely respawning ammo/health did make me play a bit more turtle-ish than I should've. I reckon I would have more fun with this once I figure out the secrets and then tried playing a bit aggressive.

2. Derelict Freighter by Paul Lawitzki
I love the aesthetics and the lighting of the map (probably my favorite in Alkaline aesthetics wise). But that isn't all, I also liked the gameplay and resource balance of the map. Playing it on hard, I was pretty low (but never out of ammo) for the first half-ish of the map. And while the map lacked a big final fight, atleast many of the small fights throughout the map were engaging, while not being too overwhelming for a blind player.

1. Dancing in the Golden Sun by Bal
The perfect rival to Arcane Dimension's Tears of the False God. AD_Tears is one of my top 3 favorite maps in AD and this is arguably ever better. While AD_Tears has more stunning visuals, I guess I like this a bit more because it is a bit smaller and thus feels a bit more... "focused" for the lack of a better word. The keys and the optional area opened from the 4 circuit boards also add to a better sense of progression. Like Tears, the open ended layout of this means I can approach the map from various methods and thus increased replayability.
I played the original v1.0 when it was out and really enjoyed it. I have now completed all the new maps in v1.2 (the ones in the separate start map room + 2 bonus maps) on hard difficulty.

I had an awesome time completing each map.
I'm amazed by the creativity, atmosphere, architecture design, map size, texture work, encounter design an other surprises. The sheer size and scale of some maps is mind-blowing with all the intricate details of the architecture, interconnections, secrets. Such detailed massive maps were unthinkable at the time Quake was released more than 25 years ago and that I grew up with.

Spotting secrets is still as fun as ever, and there are plenty of them to discover, with some great creativity in that department, often with clues for the discerning eye.

Two maps use the double and triple jump mechanic to great effect.

So congrat to the team that worked on this incredible mod of the highest caliber.
I'd pay money for this.
Alkaline's 1.2 update comes with seven new maps, as well as a sizeable amount of additional features. The reworked Cluster Mine Launcher is such a fun weapon to use on hordes of smaller enemies and the monster damage skins (even though they were already added in 1.1) do a lot to give more satisfying hit feedback across the board. Plus they just look cool as hell.

All of the new and updated maps are great, but I want to mention one in particular: Heresy's Dismal Signal Reforged has been transformed from a very good, medium-sized map in its original release to a masterpiece of gargantuan proportions in this Alkaline incarnation. The gameplay never misses a beat and the visuals are just beautiful, instantly elevating this one into my personal Quake Hall of Fame.

I also really liked bmFbr's Mountains of More Insanity with its "base map but they dug up a passage to an eldritch dimension - oops" theme. Tellus Terminus by zigi got a nice new secret Quad run, but was otherwise unchanged as far as I can tell. Still a top notch map and one of the highlights of an already stacked pack.

In conclusion, this update further improves what was already one of the most impressive Quake mods available, making it an absolute must-play for anyone looking to experience this community's finest works.
Nowadays there are only 2 real mods: AD (Arcane Dimensions) and Alkaline. AD is best for medieval, Alk for SiFi (so called base). Simple as that. There's even no competitors to Alkaline.
*There're episodes like Dwell, but that's a different story...

As for Alkaline itself, there are features that exist nowhere else. And as a modding platform it's invaluable. For clear example there's no other mod that will allow you to control aggroed monster - Alkaline allows that, and predifined chase sequences are possible in Quake with it. There're tons of unique modding features presented only in Alkaline

Well. What's left? Maps!!! Alkaline presents a bunch of SiFi maps that can be easily called best base maps existing for Quake. Tellus Terminus by Zigi is a jorney on its own - 1-2 hours jorney full of twists & secrets. Dancing in the Golden Sun by Bal may be called "SiFi version of Bal's famous Tears of the False God". Derelict Freighter by Plaw, Foundation for Corruption by Mista Heita, Geothermal Outpost by Greenwood... damn all maps are worth playing! And replaying

Best of the best
A herculean effort from some of the most talented creators in the community. A must-play up there with the likes of Arcane Dimensions.
Alkaline is a near perfect mod for base themed maps as most assets are made to fit in base theme. There are a lot of good maps included with the mod that use Alkaline assets to its fullest capability. You will be blown away by the variety that this mod provides.

A small tip for mappers: Thing to keep in mind if you decide to make your own Alkaline map is to not throw everything and a kitchen sink in. It is better to carefully pick what monsters and other assets you want to include in your level so it doesn't become jarring and overwhelming!