Elise is a lot of fun and will never get boring as she is much more comlex than other champs.

Pro:
-generally flexible because of her kit
-can be build very flexible
-incredible tower dives
-insane oneshot potential
-hardcarry potential
-can be played on the two solo lanes too
-scales good in any phase of the game if you know how to do it
-fun too learn
-high skill-ceiling (always space to improve, therefore never gets boring)

Con:
-among the 3 highest skill-cap champions in jungle (these in my experience are Nidalee, Elise and Lee Sin)
-takes a whole lot of time to learn
-doesn't forgive you any mistakes
-very high skill required to actually carry (I'm not talking about randomly getting some kills and then oneshot everyone, but actually being useful)
-Playstyle changes a lot depending on what you build

Im not going into detail with her Kit, but some information you don't notice on first sight:
-Spider Q applies on-hit effetcs
-Use Humanform W before you use Spiderform Q in order to launch the W Spider to the target
-You revive Spiderlings by using abillities in Humanform
-Ypiderlings always attack the target you attacked the last with an abillity
-You can dodge a lot of attacks when you use Spiderform E (Kayn ult, Zed ult, Khartus ult etc.)
-You can dodge towerfocus with Spiderform E
-You can jump to enemy wards and berries with Spiderform E too
-Use Spiderform and Humanform E and to get vision beyond walls
-Spiderform autoattacks are enhanced with some AP and healing. These effects do not apply on structures

Elises class is "Diver" and that says it all.
Do a blue full clear and then Red into scuttle, the other way around or only blue and immediately proceed to gank until you have no more health or enough gold for the first back (1450).
You will esoecially focus on towerdives. do a normal gank and then a towerdive when the enemy laner pushes, get behind the turret of the enemy and immediately dive when your laner pushes.
You should ideally save up your Spiderform E to Escape towerfocus.

As soon as you reach lvl 5 you can solo drake when you have two healthpotions left.(The Hexteckdrake is an exception, you need assistance for that).
You can fight for the drake very good. (change atatck focus, stun enemies, escape to berries etc.)

You can do Harry very quick. Ideally set it off after you killed someone. You then can use Spiderform W to increase attackspeed against the turret. if you were not able to kill the enemy laner yet, tower dive or stay safe with Humanform autoattacks.

After level 4 you will loose your 1st powerspike. Depending if you are ahead or not, you will haver another powerspike with 2-3 items(boots not included).

You now have a decent team fight as well as a decent 1v1, in most cases you are the win condition in teamfights.

And that is when the finisher playstyle becomes important.
In teamfights you will be the one to get the most kills. Attack with Humanform, then switch to Spiderform and if possible mainly use autoattacks and W. Save Q to finish.
Spiderform Q deals the more damage the lower the enemy is on health. This combimbined with Dark Harvest and Coupe de Grace will grant a very good finish. That is especially useful to champs with a lot of lifesteal such as Yasuo, Yone, Xin Zhao and Tanks tanks too as the Q scaling is percentage.

Even though many people say that Elise is bad lategame (KingStix even saying shes the worst lategamechamp in the entire jungle) that is absolutely untrue.
You can still oneshot most enemies. You have a stun and you can use E to dodge dangerous CC'S. You have a great scaling lifesteal (especially with Ravenous Hunter) and you deal percentage damage. you have great pressure and you are a team fight beast. Just dont build Electrocute and you will be fine.
A lifesteal/Omnivamp item will turn you into a Lategame beast.

My average wingame duration is 21 Minutes anyways.