Hello DreamWar!
Nice to see a question to a topic like this!
I will beginn with Isen vs Mordor:If we assume you play on a normal 1v1 map like FoI 1 or 2, Iron Hills, Morgai or something similar, I would start with one inside eco building (now that outsidefarms cost 300) and creep with my start batts and Bill depending on the creeps on the map and then I would go rather quickly for a Wildman-house. As soon as it is finished spam out some normal Wildmen (3-5 batts) and try to only atack the eco-building with them and try to keep them alive. But don't spam too many Wildmen so that you can go quickly for warg-building. Then build some wargs to kill the orcs.
So you have wargs to kill the orcs and Wildman to cripple the Mordor eco.
I would also go for the Palantir spell so you can keep an eye on the Mordor base and the Troll timing. When you see that he goes for trolls save up money for Sharku because he can kill single trolls and you can also help him out with the hunting arrow of you scouts and wargs to surround.
Don't forgett to buy CP-upgrades and spend the money you can't spend on units on inbase-eco or a quick Uruk-upgrade. With all that you can put yourself in a good postion and after that spam Uruks out of two barracks and build Lurtz and Ugluk, don't fogett pikes against Shelob and try to deny Cirith Ungol.
Now Gondor vs Mordor:This matchup is a lot harder in my opinion but with Gondor I would just go for either a normal barracks start or go for one inside-eco first and then go for the barracks. Then just spam swords and pikes to go creep a bit and harass the Mordor farms. After that you can either add on the very standard stables to get Gondor knights (but they kinda struggle against trolls and early Easterlinigs) or you could go for some rangers but I am realy not sure about it as they can get countered by Shelob and they force you to clump you army and trolls take the map.
So I find it quit difficult to fight against Mordor with Gondor but that is also due to the fact that Mordor is a
bit to strong at the moment.
That would be what I would do/try to do.
If you want to look for some good replays to any matchup you can also look here:
http://edainranked.com/replay_database.htmlSo far there aren't that many replays to every matchup but more will be added every day.
Best regards Smeargollum