Well I would think that online mode would be compatible with all versions because all it needs to do is send data in the same format, and why would it deliberately not do that?
I actually haven't played it since I finished the third mission, just because I've been busy, but I'll get back to it when I can.
I've been playing it on training mode, simply because this particular game is WAY tougher than most games anyway. I don't like that fact that it won't unlock all the extra missions but now that I have the preference file that does, I guess it doesn't matter. However, I can still play the new missions on training mode, can't I?
Actually the bonus missions only come in the default difficult of "Realistic", but you can't pick and choose their difficulty before starting the mission as there are no difficulty select, it just says "Start
" instead of the normal three available difficulty settings.
Basically once you beat it on training and get the hang of it, then play on Realistic and see how it goes. Just remember back in the day when the game was first out it was even harder, no cheats were even possible, no in-game savegames or quicksaves, and each level had to be completed all-in-one sitting.
But it is doable with enough practice and memorization of the level's layout and learning the enemies weakness from their behavioral patterns.
The real reason why it's hard is because they set the Aliens to respawn every so now and then, so no matter what you'll end up facing at least 2 or 3 of them every so now and then. The game wants you to keep moving and focus on your objectives rather than kill every single enemy on the level as they made it so that almost always that's impossible due to it's design of endless respawning of Aliens. But the fact that it's possible to save games now without limits help significantly for the higher difficulties.
Of all three species I have to say Alien was overall the easiest, because you just have to keep moving constantly and focusing on your objectives to reach the end of the level. There's nothing to pick up and in order to heal you have to munch on their heads. Focus on a very aggressive kind of play style. The healing bite is always instant kill but you have to position their head in the center as much as possible first.
A fully charged tail attack is also an instant kill majority of the time. Stay on the move because that blazing speed is what gives the Alien the edge. If you need to run away, you can always run towards ceilings, into airducts, vents, etc.
Predator is middle ground, can be aggressive or defensive. Against marines, aggression tends to work best with invisibility and the blades and plasma caster and since it's almost always instant kill. Disc is also perfect and uber broken and overpowered. Be on the right vision mode to lock on with it, the Disc is always an instant kill weapon, but with the lock-on effect, it also becomes homing. So homing and instant kill is just super cheap and broken, great when dealing with any big and tough enemies, marines would be slaughtered quickly by the power of the Disc. Also if necessary, you'll have to recall the Disc if it did not return to you automatically as more often than not it tends to get stuck in a wall somewhere. Otherwise, switch to the green (Predator) vision mode and look for a white object stuck in a wall somewhere to retrieve it manually. Recalling it automatically penalizes your energy resource though.
Against large groups of aliens, I see that being defensive with pistol spamming and speargun headshots and torso shots work great. Watch out for facehuggers, but pistol and plasma caster can take care of them easily due to their splash damage effects.
One-on-one way face-to-face fights, predator almost always beats Alien with the secondary fire used to charge the Wristblades for a heavy blow. Just move immediately after hitting them to minimize acid damage, never use them blades against groups of 3 or more in cramped and tiny spaces.
Be conservative with the energy supply for your equipment and weapons on the more longer and larger levels. Never forget that you don't need to look for armor items. Every blow you take automatically has been reduced by armor, which is why the Predator can sustain more hits than the other two. And don't forget that you have access to portable healing which helps, unlike the Marine whom has to go search and look for armor and healing items, Predator doesn't. Never be afraid to run away to a secure spot and heal first if necessary before getting back in there to continue your hunt.
Marine is definitely more defensive playstyle, you have to explore and look for armor and healing items and the much more better and much needed firepower to get out of every level alive. Pulse grenades can be spammed to pop those bugs quickly, best done when they are in groups of 3 or more. And it also works somewhat against them nasty facehuggeers Otherwise, always try to go for headshots or leg shots. Smartgun is excellent when facing large groups of aliens.
Against predators, you just need the best firepower, like the heavy artillery of the SADAR missile launcher, or the Minigun. They work great against any non-typical enemies you normally face on a regular basis throughout the game. The grenade launcher isn't all that great and risky to use in single player as it can backfire easily. The prox mines are the best option, frags are alright, the standard grenade is the riskiest, and it's best to stick with the pulse rifle's grenades instead.
Let me know how it goes.