Although Rock 24 takes place in a high-security combine prison and once again forces our all-time favorite hero Gordon Freeman to perform a critical rescue operation, this Singleplayer scenario never feels like a Nova Prospekt clone. From the unique introduction on board of a fishing vessel over the bizarre Prison interiors up to the showdown with a huge hangar-door opening up to a beautifully sunlit mountain scape, the campaign never looses the player in tedious puzzles, boring corridors or endless hordes of enemies.
The battles are done quite interestingly, several scripted scenes, many of which involve your fellow inmate Richard G. Newell, are fun and memorable. Some of the lighting is a bit too old-school for a HL2 map with extreme colors and blocky brush-based lights. But considering HL2's fairly grayish texture-set, the authors managed to succeed in one important aspect: The levels never look boring. Sometimes you'd wish that some custom, more colorful texturing would have been used instead of flashy lights to achieve the effect. Also the huge piles of boring crates used as a filler everywhere, some rather randomly placed props as well as very rough brush- and displacement work here and there take away from the eyecandy. Ultimately, however, Rock 24 is very good and original looking for using the standard HL2 themes.
Rock 24 has also plenty of custom voice acting. Unlike the mumbling you usually hear in user-made mods the voices are crystal clear and on par with HL2's mostly. I'm not a big fan of game-voice-acting in general, not even HL2's, but for a hobby project it's quite remarkable!
There are two bugs I encountered. One was a sentry being stuck in the elevator with the combines that caused it to never move up. The other was when Newell was giving me a surprisingly logical explanation for why we have to kill all enemies before continuing but never bothered to let go of the MG and open the door for me. Both required a reload. Although I had worse bugs in HL2 and many people won't even encounter these, that was a bit of a turn-off. But still better than having to search for a hidden switch for 20 minutes - which the authors cleverly avoided. You always see where to go next which is very important for a SP game.
If there is one thing I would have liked to see more of (in HL2 mods in general, by the way) then it would be scenes that present combine soldiers as less of a group of moving targets and more as a squad that actually outsmarts the player. The only point where I really felt like this in HL2 was the Nova Prospekt level where you set up sentries and see the combines throwing them over by sneaking up from behind or using grenades, only seeing the player himself as a secondary target. That was a powerful example of their AI system. But mostly (even in original HL2) you only see them as cannon-fodder, running straight into your shotgun, which is a real waste of potential. HL1 has a lot of 3-party fights with Human Soldiers vs Alien Soldiers vs Gordon which creates really unique scenarios. HL2 has very little of this and I'd love to see more diverse and tactical fights and less chaotic carnage between always the same combine/rebel groups. Rebels are rather boring IMO.
Rock 24 is simply one of the best SP scenarios ever made for HL2. Right up there with Minverva or the somewhat strange DayHard, which I equally enjoyed. There is room for improvement, though. It hasn't the consistent amount of eyecandy like Minerva, neither it has the interactivity of original HL(2) SP gameplay. But onsidering that the authors, Henley Bailey and Richard Acherki, basically learned mapping on the fly with this project I can only guess what excellent stuff they will produce for coming SP mods (which are announced). I hope it will involve scenes as interactive as the sentry challenge in Nova Prospekt but in a theme far away from prison cells.

Everyone who has one or two hours to spare should give this mod a try.
Design
Gameplay
Verdict
One of the best HL2 SP experiences to date. Can't wait for the next. Play it!
Pros
A nice flow, some beautiful settings and fun scripted sequences.
Design
Sometimes blocky brushwork, a few minor bugs, ordinary storyline, some repetitive combine fights