To preface this, my playstyle trends very heavily towards the "They can't hurt you if they're dead" method of thought. So, when I see a list like yours, I think...
You shouldn't be splitting the effectiveness of the Combat Squads. They need to be either shooty, OR stabby. To quote a great man: Never half ass two things. Whole ass one thing. If half of your squad is dedicated to shooting, and the other half is dedicated to melee, then when you try and shoot you're not going to cause enough damage and when you try and assault you won't win. (That is, unless you're fighting a unit that already can't handle Melee, but at that point, well... You're fighting a unit that can't handle melee. I don't know what else to say.) I would personally just take two squads with shooting capabilities, but if that's not your cup of tea, then at least take one squad with pure shooting and one with pure melee.
Also: This is a weakness in every Gladius list, but your damage output is low. You've effectively got two squads with good (*But not great) damage output and two with decent, and then the rest of your army is sitting around taking up space and peppering the enemy with very light gunfire. You really need something big, tough, and extremely powerful at your core in order to knock out big threats, but since you need to spend a ton of points in a Gladius list just to get it in working order, you really can't do that in an 1850 list without cutting points everywhere else.
If you go up against an army with lots of jink saves and mobility, (Eldar or certain Dark Angels,) or who use Invulns over armor (Daemons,) you're dead. Your shooting is simply incapable of dealing with tough targets who don't rely on straight armor saves.
Similarly, if you go up against a good Alpha Strike list that doesn't care about your first turn, you're dead. (Drop Pod Spam comes to mind.) Having your tactical squads in tanks means it'll take some creative shooting to kill them in one turn, but the problem is that three of your four threat units, (The ones that actually pose some kind of serious firepower problem to the enemy,) are going to be sitting outside of vehicles. (Namely, your bikes and your plasma cannons.)
I also don't see this dealing well with Orks or Tyranids, who can shrug off the losses that you'll inflict without giving a crap and respond by clobbering you over the head in Melee. (And Ork Warbikers double up on your counters by combining their horde-like Melee prowess with 3+ Jink Saves.) You have a lot of bodies on the field, but without being able to scratch your opponent, overwhelming multicharges will be your undoing.
However, there is some good news. Against smaller, more elite army lists, they won't have the volume of firepower to put you down. Having Objective Secured on effectively your entire army means that, should you survive to the end of the game with your troops intact, you'll be very likely to win. D-Spam will bounce off of you impotently, since you've got nothing in your army worth hitting with the D. Similarly, powerful but singular Assault units (Daemon Princes and other Monstrous Creatures come to mind) will not do much to injure you, and neither will Imperial Knights.
