One of the complaints that people have about D&D 4th edition is that it encourages 'My Precious Encounter' style DMing. That is, you spend ages crafting a beautiful encounter with complex monster powers and dynamic terrain, so your players are damn well going to encounter this encounter, whether they like it or not, whether they come up with a clever way to bypass it or not! And thus, railroading.
Here's a (partial) solution to this: instead of preparing distinct terrain setpieces for every encounter, just use a table of terrain features for each environment. Toss 2-4 dice onto the battlemat when the encounter begins, and draw in the terrain features wherever they land. Of course you can still override this system when you need to, but it's just a tool. It means not only that you don't have to put so much sweat into any one encounter, but also that you can easily relocate an encounter from one area to another if the need arises. This does have the side effect of creating a world where more or less every location is full of potentially deadly environmental hazards, but I don't see this as a bug.
City Streets (d8)
1: Winding stairs down from terrace that divides the battle area in two. Fall 10'/1d10 damage.
2: Deep ditch full of shit. DC 15 Athletics to climb out.
3: Street vendor who is angry at the combatants for driving away business. 20% chance of throwing alchemical vials for 1d8+2 damage.
4: Circular fountain 4x4.
5: Large brazier - attack roll to kick over, 2d8 damage + ongoing 5.
6: Thoroughfare 3 squares wide. Each round, 50% chance of a cart racing past at speed 8, dealing 2d8 damage to anyone it runs over.
7: Huge dungheap - anyone knocked into it it slowed and grants combat advantage - standard action to try and wipe it off (saving throw).
8: Rickety scaffolding up against a wall, with ladders. Poles have AC 15, 1hp. 20' off the ground.
1: 1d4 coffins; Athletics DC 17 to put a lid on the coffin, whereafter anyone trapped inside must make a DC 25 Athletics check to bust out.
2: Large spikes along nearest wall - knocked into or thrown onto them, take 2d8 damage and be impaled (immobile, save ends).
3: Dart trap, triggered by pressure plate, fires across room at +10 to hit for 2d6 damage.
4: Hole to lower level 2x2, with a 1-square ring around it of unstable ground that will collapse under the weight of a person. Fall 20'/ 2d10 damage.
5: Large statue, Athletics DC 12 to push over, 2d8 damage and 50% chance to pin down (save ends).
6: Bone pile, 8-10 squares in irregular shape, difficult terrain.
Wild Forest (d6)
1: Beehive hanging from tree. Can be grabbed & thrown, DC 13 Nature or Thievery to not get stung, if you hit them they get stung, stinging is ongoing 5 damage and grant combat advantage (save ends).
2: Embankment dividing up the play area. When sliding down, DC 10 Acrobatics to not fall prone. When climbing up, DC 13 Acrobatics/Athletics.
3: 2d4 thickets, 2x2 each, difficult terrain.
4: Stream bisecting the play area. 3-4 squares wide, difficult terrain.
5: 2 animate thorn bushes that get angry if anyone runs into them. 2x2, will attack at +6 for 1d8+5 damage.
6: Tarn, takes up all the space from the die to the nearest side of the map; some banks are up to 5' high, can't be climbed out except with a DC 20 Athletics, so you're better off swimming around.
Sadly, the damage expressions and hit bonii and the like are still going to become obsolete fairly quickly as the PCs' and monsters' stats inflate with every level. Sigh...