INSTEAD OF trigger, to mimic BEFORE in Oracle - sql-server-2008

Question

I am implementing more rigorous error logging into my current insert statements. I want to basically log the error that occurs for the individual row if there is one - keeping the information of the row (into a system table?). then i want to continue processing more rows. I have seen use of the INSTEAD OF trigger to accomplish this but wondered if anyone has more experience or knowledge than I can find here: https://technet.microsoft.com/en-us/library/ms175521(v=sql.105).aspx
right now I am just failing the whole insert and having to locate the error manually, I know ORACLE allows a 'BEFORE' trigger, but I have seen INSTEAD OF referenced as a SQL SERVER 2008 R2 (and above) alternative?? thank you for any help you can give!
Here is some example data to be inserted, I would like to log the second primarykey = 1 with values
(1,'five','six','seven')
as a duplicate key error, and then continue inserting rows with 9 and 0 :
CREATE TABLE ImportTable_Temp (
primarykey INT UNIQUE
,somedata VARCHAR(50)
,somemoredata VARCHAR(50)
,yetevenmoredata VARCHAR(50)
)
INSERT INTO ImportTable_Temp
VALUES (1, 'two', 'three', 'four'),
(2, 'two', 'three', 'four'),
(3, 'two', 'three', 'four'),
(4, 'two', 'three', 'four'),
(5, 'two', 'three', 'four'),
(6, 'two', 'three', 'four'),
(7, 'two', 'three', 'four'),
(8, 'two', 'three', 'four'),
(1, 'five', 'six', 'seven'),
(9, 'two', 'three', 'four'),
(0, 'two', 'three', 'four')
From other posts I have the general syntax for a trigger, but I would like to have more information about the error capture, perhaps reaching a threshold where the entire insert would fail perhaps at say 50% of the rows executed. I have seen people reference the deleted and inserted tables that are inherent in SQL Server's system tables? Is this true? How would I go about keeping track of how many errors have occurred as the process is occurring? Thanks!
--==================================================
--create initial tables for data and error logging
--==================================================
CREATE TABLE ImportTable (primarykey INT UNIQUE,
somedata VARCHAR(50),
somemoredata VARCHAR(50),
yetevenmoredata VARCHAR(50));
CREATE TABLE #ErrorTable (LogID INT NOT NULL IDENTITY PRIMARY KEY,
ImportRowID INT NOT NULL,
newsomedata VARCHAR(50),
newsomemoredata VARCHAR(50),
newyetevenmoredata VARCHAR(50),
SomeERRORValue VARCHAR(1000) NULL,
oldsomedata VARCHAR(50),
oldsomemoredata VARCHAR(50),
oldyetevenmoredata VARCHAR(50));
--=====================================================
--Creation of the Instead of Trigger with Error logging
--=====================================================
GO
CREATE TRIGGER TR_ImportTable_Insert ON ImportTable
INSTEAD OF INSERT
AS
IF ##rowcount = 0
RETURN
-- Violation of PRIMARY KEY
IF EXISTS (
SELECT *
FROM Inserted AS I
INNER JOIN ImportTable IT
ON IT.primarykey = I.primarykey
)
INSERT INTO #ErrorTable (ImportRowID, newsomedata, newsomemoredata, newyetevenmoredata, oldsomedata, oldsomemoredata, oldyetevenmoredata, SomeERRORValue)
SELECT I.primarykey, I.somedata, I.somemoredata, I.yetevenmoredata, IT.somedata, IT.somemoredata, IT.yetevenmoredata, 'Violation of Primary Key'
FROM Inserted AS I
INNER JOIN ImportTable IT
ON IT.primarykey = I.primarykey
--Insert only valid rows to the ImportTable
INSERT INTO ImportTable
SELECT *
FROM Inserted AS I
WHERE I.primarykey NOT IN (
SELECT primarykey
FROM ImportTable
)
--=====================================================
--The trigger works if I issue the command FOR EACH ROW
--=====================================================
GO
BEGIN
INSERT INTO ImportTable
VALUES (1, 'two', 'three', 'four'),
(2, 'eight', 'nine', 'ten'),
(3, 'eleven', 'twelve', 'thirteen');
END
GO
INSERT INTO ImportTable
VALUES (1, 'five', 'six', 'seven');
INSERT INTO ImportTable
VALUES (4, 'fourteen', 'fifteen', 'sixteen');
--====================================================
--I want it to work also for BULK INSERT violations
--Please comment out above statement insert and
--Uncomment below statement to see behavior I mean
--====================================================
-- INSERT INTO ImportTable
-- VALUES (1,'two','three','four'),
-- (1,'five','six','seven'),
-- (2,'eight','nine','ten'),
-- (3,'eleven','twelve','thirteen');
-- INSERT INTO ImportTable
-- VALUES (2,'two','three','four'),
-- (4,'five','six','seven'),
-- (4,'eight','nine','ten');
--=====================================================
--Select statement to view operations, if they succeed
--=====================================================
/*
SELECT * FROM ImportTable;
SELECT * FROM #ErrorTable;
*/
--==========================================================
--Drop all temp tables and triggers to allow serializability
--Execute before testing different inserts functionality
--==========================================================
/*
DROP TABLE ImportTable;
DROP TABLE #ErrorTable;
*/
Thanks goes out to http://sqlmag.com/t-sql/tricks-instead-triggers for the help with the above code!