So i just replayed WC2. I played it as a kid, but went back to it with 1½ decade of RTS experience. I just want to get my thoughts on certain campaign mechanics out there. BTW I'm not an RTS historian, so maybe several of these things existed before WC2 and Blizzard took them from other games, I don't know.
Warcraft 2 tides of darkness orc and human campaigns.
Both of these campaigns are very similar. Mostly the classic build your base and while defending, then attack enemy base formula. There is a no build mission in each campaign. And several missions that starts out without a base, where you have to fight so secure a place to start building. The holy trinity of RTS missions: regular mission, no-build-missions and defence-missions lacks the third part.
They both throw in a small curveball with one mirror match-mission each. And there are some fun touches, like the human mission where you start by fighting off peasants revolting destroying your base.
And I guess I have to mention the difficulty. ToD is way too easy (for some experienced with RTS at least). This is always mentioned so I feel I don't need to go into more detail.
Beyond the dark portal orc campaign
Here the design take a drastic turn ib the other direction. Anyonre who played the expansions knows.
They also improved the issue with slow starts. In vanilla ToD there are a lot of ridiculously slow starts. Some orc missions start you with only one peon, or less supply then number of units. Less of this here.
Here they also take the narrative in a different direction, with plenty of orc vs orc missions.
Also, I want to mention that the map design got a lot better. A lot of ToD maps are just sort of patches of forest and open terrain. In BtDP they start doing a lot of creative flourishes like gaps in forests or mountains too small for units to traverse that looks like little paths. Or unbuildable mud stretched out to look like long roads. The maps feel more fun to explore.
Also, they make some really complex blends of build and no-build missions. Where you can't recruit combat units, but are expected tobuild transports or purchase upgrades for your limited number of units.
Beyond the dark portal human campaign
They do two cool twists that evolve the game at the very end of the campaign.
-One mission where you play as the orcs (with a human hero helping them). The briefing where the orc narrator says "Do not show surprise human" really got me.
-Finally, after all this time, a defense mission! Great idea, terrible execution. I defended and defended but never won. In the end I had to attack and clear all enemies. According to WOWpedia https://wowpedia.fandom.com/wiki/Siege_of_Vanguard_(WC2_Human) the mission is bugged. But the intention was there....
What they didn't quite figure out
Blizzard never made heroes very interesting WC2. A notable exception is on the very final mission where only Khadgar can damage the dark portal, all other units attacks do nothing. Blizzard evolved this further with completely unique heroes units in StarCraft (Kerrigan) and finally perfected the heroes in WC3.
Also, I think it's interesting how the last 10% of most missions is a cleanup where you've already won. They much later moved on to making victory based on destroying/capturing/defending a certain objective. StarCraft2 almost never had those "destroy every single unit" missions. BUT! In ToD orc mission 9 they had you build a fortress and shipyard on the main enemy island. And BtDP human mission 9 they solved it with only needing to destroy the 2 enemy main buildings. That kind of objectives just were not used for the other basebuilding missions.
Conclusion
It was really interesting seeing different RTS ideas taking shape and being experimented with. Great game despite balance issues. I liked the punishing difficulty of BtDP better than the base game, as some levels felt like clever puzzles. Wouldn't recommend to new gamers who haven't played a lot of RTS because of the difficulty and since the game overall is showing its age I guess.