So, I was in an argument with a fellow player and Dungeon Master, over why his system of choice (Legend) isn't as "tactical" as 4th Edition. It's kind of an odd argument, as I'll concede that a lot of it is intuitive. But the biggest thing I took away is this: less is more.
If you think about Chess and you think about Dungeons and Dragons, which is more complicated? Rules wise, Chess is significantly less complicated. But the fact of the matter is that, the game is entirely based on positioning-where you can move. But where you can move is the counter-point to where you can't move. So, where am I going with this?
4th edition assumes a grid. Every game mechanic is built with this in mind, from the way auras and bursts are described to range and reach. And moreover, the simplicity of Square Fireballs (my apologies to Perico) ensures that the consequences of positioning are obvious, compared to circular bursts. The obviousness and simplicity of how game effects are defined allows for the implications to be defined-meaning that the mental calculus for how the game plays is something actuall doable. Certainly, in a "twenty foot radius" burst scenario, characters know to "fan out," but doing the square by square count of "are we safe?" is more troubling.
In 4E, positioning is a thing. It's not just a question of "are they close enough to catch them both in the same attack" or "are they in melee range." And it's this element of positioning that makes Forced Movement such a powerful effect. Drop "move an enemy five squares" into a previous version of Dungeons and Dragons, and it doesn't have the same level of effect. But the implications of 4th edition aren't merely about hindering terrain-they're about ensuring enemies are in the exact spot you want them to be.
In 4th edition, no one really understands "What is a controller" and "what does a controller do." Oh, we all know controllers have forced movement and area attacks and status effects... but so does every other class. As someone who has played almost exclusively controllers, I can tell you, there is a methodology behind control-the complete understanding of the arena. Whenever I start an encounter, I don't simply think "who am I going to attack," though that's certainly true as well. No, my first thought is "where are the enemy, and where do I want them to be."
More to the point, it's not just controllers that are tactical. Numerous monster abilities make heavy use of the grid as well. The "doughnut" aura effect is an interesting example, wherein an aura is more powerful at a longer range than at a short range, and enemies can have forced movement-or even forceful teleportation as well. So many of the better monsters are built not just in the concept of "how can we make this damage the PCs" but "how can we make it dangerous for the PCs to engage this enemy."
1.) Positioning is more limited, which is paradoxically more freeing; tactics in games is intrinsically related to predictability.
2.) The game is centered around using the grid.
3.) Characters just have more options, from level one up. Sometimes those options don't matter, but even the simplest builds have at least two choices in virtually all circumstances, and often three.