People don't seem to grasp the niceties of 5th edition, and keep running (and posting) 4th edition lists.

I hope to point out a few simple things that everyone needs to know.

5th edition basics:

Shooting:

Killing tanks is very difficult, due to potential cover saves and a unified table causing hits to only do limited damage if you have no modifiers. Killing infantry is very difficult, due to cover saves being improved to 4+ and everyone getting it.

You need to negate cover saves versus infantry, and you need to pound infantry with wounds to make them take so many saves they get annihilated. You need to hit tanks with AP1 weapons, or barring that...hit them with a ridiculous amount of shots to attrition them away.

Assault:

Assaults are much more difficult to survive as each wound you lose by is a -1 modifier to your morale check or a armor save you have to take (if fearless). Now that consolidating into new units is no longer allowed, it's dangerous to assault someone suckering you with a cheap unit in the open--because when you kill it, he shoots you to death his next turn.

The purer assault armies, Demons/Wyches/Blood Angels, suffer from this issue. They ARE overwhelming in CC, but with a few sacrifices they can be stopped. The 'standard' build of most armies is one assault unit in reserve. Well, that's pretty easy to ignore now, because you can sacrifice fly one unit to it then shoot it to death. Still good for counterattack, but a charge? Usually just suicide.

Movement:

With these things in mind, bringing lots of anti-marine firepower will generally net you a loss against everything but marines. People are starting to figure out that anti-power armor builds (meaning low AP weaponry in huge amounts) are a fail, and terminators/marines will generally ignore cover (they should) and instead run around in the open. This gives them a mobility (no difficult terrain tests) that normal infantry armies do not have (have to sit in cover usually, so they have to take difficult terrain tests). So the reality is, marines get a 6" + D6" if they want to, and usually other armies get a 2D6" pick the highest + D6", so marines are on average able to get further on foot than other armies.

Fast vehicles are still uber. More fragile, yes. They are able to pound you into the dirt though. Land Raiders fall somewhere between normal and fast vehicles. They are not fragile, and they can pound you into the dirt too. Normal vehicles (meaning, not fast) can cripple your army if you setup 24" away from a rhino rush and he goes first. Move 12", deploy 2", rapid fire you. Always setup further back when facing armies like this, so you don't get alpha striked.

Setup:

Setup is probably the most important thing. If you cannot redeploy your army quickly, you need to go second and setup as if he's going to go first. I can't tell you how many times I've had an immobile gun army facing a mobile player (but not a fast skimmer army) and setup in a corner and killed his army piecemeal. If you aren't Orks, Eldar, or Dark Eldar...don't setup in a line and expect to do anything but piss and moan after the game.

That should about cover the basics of 5th.