Starcraft 2 - worth buying?

[Archon_Wing]

The ladder system is pretty good at finding you a good match for the most part. The beginner's maps don't really help very much because the rocks make it a completely different game, (strong terran bias typically) You'd probably benefit more by playing vs the computer which is actually a bit challenging on hard/very hard mode for a beginner and might be stronger than some players you'll come across.

Also, I would check out the single player challenges, very useful in teaching new players too. Those will help out new players much more than the practice league as it'll show them situations that will happen in your typical game.

Oh I'm not a new player. Although it has been a good 6+ years since I had played a match of Starcraft prior to this. Played a ton of Warcraft 3 in the midterm.
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Well it is a very different game, interface, units and all. Plus everything is very mobile which changes the whole pace of the game. Prior experience does help, but it will take a while to learn stuff.

For the life of me I cannot get the gold for the initial Zerg survival mission, best I've done is 15 lost units.

The challenges? Yea, that one is quite annoying. The best thing to do is to use the infestor and a few zerglings vs the immortal (just use use neural parasite). Also, 2 ultralisks are all you need against stalkers. Against the void rays you want to burrow hydralisks and unburrow them once they begin to fire on the pylon. Using a lot of burrow will help minimize losses.