Firstly, and this helps Blood Angels & Grey Knights too, combat squads from the same parent squad can ride the same transport. Awe. Some. This opens a variety of tactical options and although the basic Tactical squad is perhaps not as good at this as Blood Angel Assault Marines, it's a great, great option for squads which can use it.
Secondly, Combat Tactics is so much better now. Without the ability to escort units off the board (i.e. even Marines can rally within 6") and Random Charge Length, combat tactics is now a great ability which is basically going to divert firepower away from front-line squads unless the opponent forgets (this will really only happen max once against each opponent). This is also really useful in combat as Marines aren't really at their best there with 1A base. Although the basic rules allow any squads to flee against something they cannot damage, Combat Tactics can be used anytime a morale test is required and thus has a lot more flexibility.
Beyond this, the usual Marine changes apply here. Improvements to Rapid-fire weapons are great for the likes of Tacticals/Sternguard. Cover reduction and the general increase in AP2 weapons means Marines are going to be less survivable against weapons which ignore their armor but are still quite durable against small arms. At the same time, this cover reduction helps the Marine shooting, and they are a shooting force make no mistake. Which leads to the impact of RCL - Dreadnoughts with their general immunity to Overwatch firepower become quite scary though their main combat unit, TH/SS is okay with it - the shorter general charge ranges suck but they have the durability to shrug off most Overwatch firepower and TH/SS charging 7"+ is scary. The combination of Combat Tactics, Overwatch & RCL means Marines are also pretty decent against assault based units as well.
One of the big boons for Marines is the increase in relevance of some of their characters.
Pedro - Rapid fire weapon improvements and cover reduction makes Sternguard an even better swiss army knife. Making these guys scoring so you don't have to take more than two big Tacticals rocks and BA allies can bring a 4th squad. Still losing Combat Tactics though...
Lysander - challenge beat-stick. Break him if you can. Adding in a bolster defenses and bolter drill are gravy on this which ensures the army can benefit as a whole. Again, Stubborn for Combat Tactics.
Shrike - Fleeting TH/SS are scary. That's all that needs to be said here.
Khan - hit & run on whatever squad you want, Outflanking combat squad units in Rhinos, etc.
Vulkan - Still good with twin-linked melta & flamers for Overwatch goodness. TL-snap fire melta k.
The others remain basically the same so let's look at a few of the Vanilla option stand-outs and new duds.
Libby is still a solid choice though no Divination discipline sucks (mainly for Tau allying really). He brings some good spells (augemented by the new rulebook powers) and psychic defense utility. Still far outstrips the Chapter Master and Captain except on a Bike who is a good challenge beatstick. Bikes in general as a full army are a bit weaker though with cover reductions by a Hybrid force is still viable it seems. Command squads without a 2+ save are less of a deathstar options than before with combat & FNP changes though true T5 is nice.
TH/SS & Dreadnoughts as said are very good assault options as they can generally ignore or suffer through Overwatch and aren't going to sneer at getting those 7" + charges. TH/SS in particular love Shrike. Shootynators are much improved in combat with less options capable of breaking their armor and they still bring good dakka and likewise shrug off most Overwatch shooting. Sternguard with rapid-fire and cover changes are an improved swiss army knife and with combat tactics, full squads can be very scary from Rhinos.
Tacticals are still a sort of Achilles heel - a good unit but not something which you can take six of. With Allies though running two full squads is a much more viable option. Rapid-fire + combat squads are big boons here as well as snap firing allowing melta-bunkers to remain a bit more mobile. Scouts are still a token scoring backfield unit really.
Bikes & Speeders are still solid options both with Speeders capable of bringing double-MM to bear quickly though with only AV10 and two hull points, are weak to lots of firepower downing them. Bikes are true T5 so not going to be instant-deathed as usual and with Snap-fire + Flat Out moves for vehicles, Bikes can hide a lot better with the slower vehicle chassis compared to before.
AV13 makes Preds even sturdier at range unless versusing Tau or the like. The vehicle changes could make ACLC Preds more attractive but they are still pretty static and Dakka Preds put out nice firepower which with the cover changes, can chew through hordes quite quickly. The Thunderfire has upped in value with its improved durability and S5/6 blasts being a bit better against vehicles. Land Raiders with AV14 have a lot more tactical application options, particularly at range and with hull points are less likely to be one-shooted or immobilised early. Still cries at the sight of multiple meltas though.
Overall the bad units stay bad (with a few exceptions like Thunderfires) and the good units got some general boosts. The real take home message is the special characters are a lot more usable and this opens up build options a lot as well. Add in Allies to bolster the scoring power of the 2x10x Tacticals and Marines are much better equipped to overcome some of their issues seen in 5th.