Advantages/Disadvantages of electronic viewfinders have been discussed in another question for completeness:

• Optical TTL viewfinders are pretty much as sharp as the lens (with small losses for the focus screen and prism). Electronic viewfinders have fixed resolution, which is currently lower than OVFs.
• OVFs update in realtime, EVFs have a fixed latency and refresh rate (time taken to process the image, number of updates per second).
• Coverage of OVFs is often less than 100%, eyepoint & dioptre adjustments are limited as is the apparent size and brightness of the viewfinder.
• Electronic viewfinders have the ability to preview colour balance and depth of field (without darkening the image), zoom the image, apply gain for night shots as well as the potential of overlaying a limitless amount of metadata (gridlines, live histogram etc.).

The principal advantages of an SLR (or SLT) system are

• Ability to have TTL viewfinder! (see above)
• Ability to direct light to phase detect AF sensor.

The disadvantages are:

• Size / weight
• Shorter backfocus distance, allows more compact wideangles, as well as mounting of a wide range of legacy lenses.
• Increased reliability (fewer moving parts).
• Noise / Mirror slap (causes motion blur)
• Shooting speed (no need to move the mirror).

Once EVFs match the resolution and refresh rate reaches the level where it is not noticeable is reduced the advantage of SLR systems slips away rapidly. Currently phase detect AF is superior to contrast detect for locking onto and tacking moving targets, but CD AF is getting better and manufacturers are working on including PD sensors in the main pixel array.