Space Marines are the secret sauce of Games Workshop.
If you play Warhammer 40K there is a good chance you play Space Marines, are thinking of playing Space Marines or will be playing Space Marines in the next year…
So what makes them such a solid army besides being at the front of the line for every new release and book?
A few points in my experience, in terms of army wide effect vs. selecting specific units that make them a STRONG army.
Army wide T4 and and an armor save.
Most dice rolls will be wounding you on a 4+ (50/50) and you are always going to get some sort of a save, even if it is a 6+. This gives them an army side base of suitability- especially with 40K being a D6 based system, one is subject to wide swings in the dice.
You can’t rely on it, but you there will be times you make a ton of 5+ save in the unit and your Marines live to counter attack when your opponent planned otherwise.
I also consider the good base leadership and And They Shall Know No Fear a huge army boost- Marine players get used to having such an amazing anchor with your Marines not running away or acting in ways you don’t want.
Layer over Chapter Tactics and you can customize your “chapter” in the moment- yes blue colored Space Marines can play around with different Chapter Tactics…
…and finally some powerful psykers and psychic support in the game- better or equal to many of the other armies in 40K.
These four give Marines a HUGE anchor and base of tactics before one even starts leveraging unit specific tactics.