It's long, it's fun and it's more half life with content from all the expansions. Field intensity is a really good half life mod that puts you in the role of another soldier during the black mesa incident.
The difficulty is just right, this mod's levels floods you with enemies, and you will have just enough ammo to kill them all.
the squad system expansion helps with the enemy count. you now have as many companions as you want, who will help you fight.
This mod also features voice acting with pretty good quality for the story bits, it's not professional level but it's still really good, especially for mod standard.
I would say the level design is perfect but I did find some places during the early-mid maps that were all too similar to each others. However mid to late levels are all really well done, with lots of puzzles and platformer sections that never become too frustrating or too easy.
This is easily a must play for half-life 1 fans.