You see this a lot in casual gamers or on forums - Warhammer 40,000 isn't a tactical game. There is not grand strategy behind your army or individual games and the rules don't support tactical play. Other games are generally then brought up as 'better' examples of tactical or strategic tabletop games. I cannot really comment on these other games, other than Fantasy and to some extent Warhmahordes, but won't bother. Whether or not Warhammer 40,000 is less tactical than these other tabletop games is irrelevant because the premise of Warhammer 40,000 is not a tactical game is flawed.
Let's look at this with just a bit of logic. General > list. This is a pretty commonly accepted belief and assumption of any game. Whether it's a build strategy in an RTS game, character build in a RPG or a specific army list for a tabletop game, it doesn't matter if it's the most awesome thing since Chuck Norris if the player behind it has no experience with it. There are some point and click versions of things certainly and in some games these can be very effective. Guild Wars PvE jumps to mind (Sabway k thanks) but Warhammer 40,000 is anything but point and click. This is where this assumption of 40k not being tactical breaks down.
First we commonly see the same people/forums who say 40k isn't tactical disparaging against 'netlists' and the like and especially when they do poorly. Oddly enough this goes against their argument as it supports that general skill, ergo some tactical ability beyond target priority, is more important than the list itself. We can see this in prominent players such as Tony or MVB who both have had excellent success with lists which are seen as good but not 'fully netlisted.' Coincidence? No, I think not.
So where then is the actual tactics of 40k? We have the over arching strategy generally developed around the army list you are using, the opponent you are facing and the mission you are playing. Whilst some armies can play in a very similar vein against every list in every scenario, many do not and are generally better with tweaks to their overall strategy in different scenarios. For example, think about what we discussed in the recent Reserves articles and when your whole army reserves and when it doesn't. Classic example of extreme strategy shift. This overall strategy generally outlines important targets in your opponent's army list and locations on the battlefield (i.e. objectives) and will thus dictate target priority and the execution of your tactics during the game.
And this is executed through movement - games are won and lost in movement. Dice can certainly alter this but dice have the least impact in the movement phase. You can move up to a set distance with each unit and engage in specific actions depending upon how far you move. Only a few things such as terrain and opposing units can disrupt this but even with those in mind, you have the most control over your own movement. Lists which are subjected more to your opponent's whims in terms of blocking will therefore find themselves at a disadvantage and armies which can overcome such blocking more regularly, have an advantage. What this paragraph is getting at is YOU have control over what happens in movement and there is little to no dice effect upon this. As we know, you can play everything perfectly and then miss with everything or fail to make a save but movement can ensure this impact is as small as possible.
Movement is so important because of this control. Not only does it set up the shooting and assault phases thereafter but it's where you have the most control to impact your opponent's movement with blocking. You obviously have this ability in assault due to assault moves and consolidation but you have more control of this during the movement phase as you are more capable of moving faster and to any location you want with more units. This is also where threat ranges come into play and how they impact the game and not only yours but your opponents. Armies which revolve around 24" for example are all about movement and maintaining that 24". You want to keep your army between 18.1" and 24" from your opponent to avoid most assaults and shooting whilst maximising your output. Your opponent wishes to close that gap. You manage all of this during your movement phase and this significantly impacts the amount of damage you or your opponent can inflict in a given turn.
Conclusion
And this is where the ultimate tactics of 40k lie. There is obvious strategy involved in regards to army list building but generalship is always going to be more important. Not only does this strategy of list further need to be applied to the tabletop but each turn brings multiple decisions which need to be made. Some of them such as target priority are quite easy comparatively but movement is most certainly not. Having 360 degrees of options in terms of direction of movement with the added complexity of facings, ranges, potential distances and different actions/benefits/disadvantages more moving slower or faster generates a lot of tactical flexibility and options for each player. Add to this your movement can disrupt your opponent's army or movement in turn whilst impacting the amount of potential damage an army can do in a turn and you have a tactical game.
This might not be as tactical as other games out there, I don't have the knowledge to dispute this but you can obviously make 40k more tactical. As it stands however, it's not a point and shoot game or a game devoid of tactics and anyone who thinks so is fooling themselves. Just like with poker, there may be a certain amount of luck involved but skill overrides this in terms of consistently winning. That's why there are top poker plays and that's why we can see some people do consistently well, often with different lists. And this stems from the tactical aspect of the game.
