I enjoy turn based (TB) squad level tactical games such as X-COM and have done for many years, but I feel that the "tactics" tend to be more dependant on the round system than the combat situation in the game world. While positioning your units and deciding their actions in these games is far more important than most other genres - those are some of the reasons why I enjoy them - the games tend to be more about saving Action Points (APs) or Time Units (TUs) for use in the enemy's turn than the physical combat situation you're units are currently in.
For example, a particular situation will play out very differently if it occurs at the end of the player's turn than at the beginning, even if the position and physical parameters of every entity in the game world is identical. This has been described as the difference between tactics and gameics.
While some players may enjoy this particular aspect of TB games, I would personally prefer to use tactics borne out of the game world instead of the control system, and would like to see a tactical system which eliminates the dependance on an arbitrary round system and the sequential unit action model which necessitates it.
The Concurrent Action Tactical Simulation (CATS) document details my particular take on a control system for tactical games where all characters in the game world move and act concurrently. The ideal of this system is that the player can review the current situation and update unit orders without being limited by how much time is spent considering each unit's situation or possible actions.
For more details see the CATS document and several examples comparing CATS and sequential TB systems.
The non-sequential style of tactical game is still very young, but hopefully games such as UFO:Afterlight, Brigade E5 and Titans of Steel: Warring Suns will bring a better understanding of the genre to gamers and promote its continued evolution.