The role of deployment has changed quite a bit with the advent of 5th edition. There was a time when you coukd setup a serious gunline and blast away. Back then a game could well be decided by whoever got to go first. To me these were the most boring games and could be tough to win. I rarely ever play gunline but I have, mostly with Dark Angels or vanilla SM prior to the release of their new rules and 5th edition. Now the ability to hold your entire army in reserve really can befuddle any opponent running a gunline army. Cover saves have also hurt gunlines. I am all for the new rules and think the more dynamic 5th edition has been a great change for the game.
Deployment is still very important and I think it's still the most important phase of the game. Look at this way, a bad deployment can kill you before the first dice is rolled. I believe an army should always be deployed such that your units can support each to the hilt. Tyranids have always been about sending in several waves... Tyranid players that can't grasp this important concept rarely if ever win versus a good player that recognizes the Nid army was hastily deployed. Nidz are pretty much designed to be played in waves with synaspe. One big change is how does the Nid player go about using their troops. I see a lot of outflanking genestealers, it sounds like a good idea but it is random in that your bugs might come in on the wrong side or your opponent simply castles in the center position of their DZ
Back to first turn and gunlines before 5th edition. I remember reading a batrep from an old White Dwarf. This was back when the studio produced goof batreps with complete army lists and it wasn't decided prior to the game who would win. The mission was victory points and the two armies were guard and dark eldar... More to come soon!