As an old Rogue Spear veteran, playing nearly every Rainbow Six in the past 16 years, I have quiet a lot to say, that's why I'll sort what I have to say in to a PRO/CONTRA list.
PRO: After finishing the tutorial, you will be able to control your team,your equipment and will have enough tactical basic knowledge to actually understand how the game works and how to master your first mission. There is a massive option on weapons in this game, Assault Rifles,Sub-machine guns,Pistols,Machine-guns,Sniper rifles, grenades, explosives, electronical kits, technical equipment as heart-beat sensors and much more! You have 3 different types of clothing, Light,Medium,Heavy in many many different camos/colors. You have a big option of team-members you can pick how you want to, each member has also an own CV + Health datas ( eye color, age, size,weight ) and each team member has own advantages and disadvantages. Every team-member you can pick, has an own specialisation skill ( Electronic Specialist,Assaulter,Sniper,Surveillance,Explosive specialist ) Since you can pick specialists and can create your team how you want to, you COULD for example create the perfect team and also choose equipment for each team-member. You have a very good " Mission-planer " before each match, where you can set waypoints and more. The campaign is made pretty nice, interesting story, good spoken and written, pretty realistic AIs ( Terrorists and Hostages ) and very nice large to medium sized maps. There is also a multiplayer which is dead without using programs like GAME RANGER or others, there are quiet a lot of mods for this game you could use and also packs like Athena. The Graphic is pretty good ( Check screenshots in gallery ).
CONTRA: There is really nothing negative, except a few things. You can't zoom in to iron sight, iron sight does not exist ( only with mods ) but you can use your scope ( if mounted, some rifles already have an integrated scope, like for example the G36 ). Multiplayer is kind of dead ! But there are some players in forum, who say they play multiplayer. But I've been never really playing Multiplayer in 16 years I play Rainbow Six games, because Rainbow Six is very enjoyable and never boring even in singleplayer. Sadly the game has no " special effects " like massive blood massacres and bullet holes in human bodies, you only can see bullet holes in walls,glass,metal. I can't think about bullet holes in your enemies, like it was in rogue spear. Blood does hit the wall when you kill an enemy standing next to a wall though !
Well, I hope it wasn't too much text. Rainbow Six is DEFINITELY a MUST for every tactical fps player! This game is the TITAN KING of all tactical FPS games, not to compare to games like CS,CoD,Battlefield. This game has similarities to SWAT 4 though !