Call Of Duty 4 : Modern Warfare
The perk is very useful in close quarters levels, as well as small rooms where it is difficult for the enemy to exit in time to escape the blast. In multiplayer, some servers on the PC version ban the use of Martyrdom, either for it being considered cheap, or that it can become annoying if many/all of the players on a server have it, though many also argue that the inclusion of this perk is simply part of the game and can be easily avoided by more experienced players.
Though it's not a reliable perk, Martyrdom can give the user a handful of additional kills. Most players now will assume that a player has Martyrdom and flee the area as soon as they achieve a kill. Confined areas and Sonic Boom makes this perk more effective. It should be noted that some servers will kick players using this perk in the PC version of Call of Duty 4. It is also frowned upon to use in Hardcore Team Deathmatch and Hardcore Search and Destroy, given that the dropped grenade can also kill teammates (thus it is far rarer on those modes). However, it can still be useful against enemy players because they won't be expecting martyrdom and there wont be any grenade indicators so players still sometimes use the perk in those modes, and due to decreased player health, the perk becomes much more effective if teamkills can be avoided.
Many players despise Martyrdom as it is considered to be cheap way to earn kills since there is usually absolutely no skill required, and one is basically rewarded for dying. However, Martyrdom can also be used tactically, such as a with an SMG. Some players even use Martyrdom as a suicide bomb by running into an enclosed area with enemies and allowing themselves to be killed in hopes of taking down one or more enemies. It is often thought that even having the fuse lengthened by a second would make it more fair.
If you are quick to react, it can be very advantageous to throw an enemy's Martyrdom grenade if the grenade was just dropped, so you do not need to run away and risk exposing yourself to fire, and you can get kills with it. However, be ready to sprint and/or move backward once an opponent is eliminated. If there is a threat of running toward more enemies then try move around a corner or go prone behind something. Turning completely around may take too long and there is a good possibility you will be hung up on another teammate.
There is also a tactic with martyrdom that can get quite "explosive" and is deadly with one person, but can be devastating with a full squad: Primary Grenades x3, Sonic Boom, Martyrdom.
This is a powerful tactic but this tactic is known as Grenade mortaring and is thought to be very "noobish" and should not be used on hardcore as it can be very easy to kill your teammates by mistake.
Call Of Duty 5 : World At War
Martyrdom reappears in Call of Duty: World at War just as it did in Call of Duty 4: Modern Warfare. There is no superficial difference between the two perks from the two games, as both grenade times are 2.5 seconds. The only possible difference would be that the grenade indicator for Call of Duty: World at War dims down when you are further away from a live grenade (Treyarch developers have changed the effect of grenades). Thus, the dimmer the indicator, the less damage you will take. This is not true in Call of Duty 4: Modern Warfare as even if you are at the minimum range of the martyrdom, you would still get killed. Due to this fact, it is much easier to escape from Martyrdom in Call of Duty: World at War, as the player that killed the Martyrdom user will usually end up backpedaling. As with Juggernaut this is a considered a very "noobish perk", especially in Hardcore (due to the lack of grenade indicator). Some servers do kick players who use Martyrdom.
Note: The Martyrdom grenade on Call of Duty: World at War can be picked up and thrown away, causing little damage to you. However, it must be done within a very short period of time (2 seconds at the most) to ensure survival).
In the Single Player campaign, if you injure an enemy, and they go down, they are capable of several things, including Last Stand. Some enemies will actually pull the pin on a grenade and blow themselves up, and hope you get killed too. This is because some players may spray and not be aware of a dying German and will kill the player if in close proximity, even on Recruit.
Call Of Duty : Modern Warfare 2
Martyrdom is a Deathstreak in Call of Duty: Modern Warfare 2. It requires four consecutive deaths before it can be used (three if using Hardline Pro), so it is seen far less frequently than it was in previous games. It is also weaker, as the grenade fuse time has been increased to that of a normal grenade and frag grenades were made weaker in Modern Warfare 2.