After playing a while I have some suggestions and reguests too.
At first a point to the Lictor. He can capture the objectives like all the other Tyranids and I think this is fine. But he shouldnt stand invisible, when he capture it. Sometimes it is very easy to get a stealth win. Make him visible if the player use the use button. So the Space Marines have a chance to respond to him.
A second thing is the balance of the classes. I love all Tyranids classes. Every class has its own mission area. But I have problems with the Carnifex at the moment. He is a realy scary monster for all tactical marines and he has no problems to kill 3 at the same time.
But against melta, heavy bolter or terminator he dies pretty fast. I would like to see him in the tier 3 class to give him the recognition which he deserve. Make him tougher against these weapons.
I read a lot of reguests for an apothecary marine. I love this idear too. Maybe some of you knows the game killing floor. The players can heal each other or themselve with a syringe. The players dont get the full healing immediately but over a time and only 20 health per injection. This is only an example but I like this way of healing.
The apothecary marine could be a tier 1 class and is carrying a boltpistol and Chainsword combo. Not very dangerous against the Tyranids, because he is a supporter class.
I think the reason why the people would see this class ingame is that it would promote the teamplay between the space marines. My personal opinion is that a apothecaries marine give the space marine a better chance to charge. A lot of time, when you get a contact with a Tyranid you die or left this “meeting“ with very less hp. And if you go to the next objective you die very quickly without to reach it. Thats very annoying if you have an expensive class.
Naturaly the Tyranids should get health regeneration too.
What is with the termagaunts. I readed that you get problems with his animations. But it works with the stealer and looks very good. Are they so different of her anatomy?
The termagaunts could be the shooting class for the Tyranids. More accurate than a warrior, but less damage and maybe no option for a compat weapon. But his health and movement speed could be the same like the stealer, except his jump attack. Yes I know that the warrios take that part with his inaccurate but stronger weapon. Maybe push him to tier 2 and give him a little bit more health.
So all bigger Tyranids are in the higher classes and a player who see them knows that they are the stronger one.

In consideration that the apothecary marine and the termagaunt get into the game I see this tier chart.
Tier1
tactical marine / apothecary marine
stealer / termagaunt
Tier2
veteran marine / special weapon marine
Lictor / Warrior
Tier3
heavy weapon marine / terminator
Zoanthrope / Carnifex
Please excused my bad grammar or my coise of words. Its my first time since long that I wrote a huge text like this in english. I hope you understand my points.